Lightweight co@N-pyc / mxene-BC wave-absorbing aerogel and preparation method thereof

Abstract

The application relates to a light Co@N-PyC / MXene-BC wave-absorbing aerogel and a preparation method thereof. The material comprises a Ti3C2Tx nanosheet matrix, a pyrolytic carbon layer and metal cobalt particles are coated on the Ti3C2Tx nanosheet matrix, and bacterial cellulose is added to assemble a Co@N-PyC / MXene-BC aerogel. The aerogel coats dopamine and cobalt particles on the Ti3C2Tx matrix through in-situ self-polymerization. After heat treatment, a nitrogen-doped pyrolytic carbon layer is formed on the surface, and a large number of defects are introduced. In this way, the dielectric loss can be enhanced, and the density can be kept low, so that the wave-absorbing performance with low density and high loss is realized.

Description

Technical Field

[0001] This invention relates to the field of microwave absorbing material preparation technology, and in particular to a lightweight Co@N-PyC / MXene-BC microwave absorbing aerogel (lightweight nitrogen-doped Co-confined catalytic Co@N-PyC / MXene-BC aerogel) and its preparation method. Background Technology

[0002] Since the advent of the wireless communication era, the application of electromagnetic waves has become widespread. However, this has also brought electromagnetic pollution, posing a potential "hazard" to human production and daily life. Therefore, the development of efficient and intelligent electromagnetic wave absorbing materials is particularly important. Absorbing materials should possess the performance characteristics of being "light, thin, wide, and strong," and absorbing materials with low density and high loss characteristics have significant application prospects. Due to their excellent properties such as low density and high strength, porous lightweight electromagnetic absorbing materials have significant application potential in the aerospace field. MXene (MXene-based two-dimensional titanium carbide (MXene)) is widely used in electromagnetic wave absorption and shielding due to its excellent conductivity. Because MXene nanosheets are small in size and have weak interlayer interactions, it is difficult to construct stable three-dimensional foam structures. However, constructing three-dimensional layered structures through various means is an effective way to fully utilize the highly conductive MXene nanosheets. Compared with MXene nanosheets, lightweight three-dimensional foams made from MXene nanosheets have low density, good flexibility, and a porous structure, providing favorable conditions for multiple reflections of electromagnetic waves.

[0003] Optimizing impedance characteristics is key to achieving excellent electromagnetic wave absorption performance in materials. For high-loss materials like MxeneTi3C2Tx, the high conductivity causes a significant difference between the material's impedance and its spatial impedance, leading to electromagnetic wave reflection. Therefore, it is necessary to select a low-loss dielectric to balance the high loss of Mxene and allow as much electromagnetic wave as possible to penetrate the material's interior, thereby optimizing electromagnetic wave absorption performance. Furthermore, interface engineering is an effective strategy for controlling dielectric loss; it can enhance electromagnetic wave attenuation by regulating the movement of charges between interfaces. Dopamine can self-polymerize to form polydopamine under aerobic conditions. Due to the presence of active groups such as hydroxyl groups on the surface of the coated material, polydopamine (PDA) can adhere to any matrix material. Moreover, PDA has the property of forming coordination polymers with metal ions, allowing for in-situ metal deposition without electrodeposition or co-deposition with metals. This coordination polymer can be converted into a highly conductive pyrolytic carbonitriding material (N-PyC) after high-temperature pyrolysis. Therefore, this strategy can be used to construct heterostructures to enhance dielectric loss capabilities.

[0004] Existing methods for preparing microwave absorbers typically involve loading metal particles onto the microwave absorbing substrate using hydrothermal or electrodeposition methods. These methods are complex and prone to particle detachment. Furthermore, introducing nitrogen doping into microwave absorbers usually requires an external nitrogen source, which is cumbersome and makes it difficult to control the amount of nitrogen introduced, resulting in uneven nitrogen distribution. Summary of the Invention

[0005] To address the aforementioned technical problems, this application provides a lightweight Co@N-PyC / MXene-BC high-loss absorbing aerogel. This aerogel encapsulates dopamine and cobalt particles onto a Ti3C2Tx (titanium carbide) matrix through in-situ self-polymerization. After heat treatment, a nitrogen-doped pyrolytic carbon layer is formed on the surface, introducing a large number of defects. This not only enhances dielectric loss but also maintains a low density, thereby achieving low-density, high-loss absorbing performance.

[0006] To solve the above-mentioned technical problems, the technical solution adopted in this application is: a lightweight nitrogen-doped Co-confined catalytic Co@N-PyC / MXene-BC aerogel, the material comprising: a Ti3C2Tx nanosheet matrix, on which a pyrolytic carbon layer and metallic cobalt particles are coated, and bacterial cellulose is added to assemble and form Co@N-PyC / MXene-BC aerogel.

[0007] Furthermore, the density of the Co@N-PyC / MXene-BC aerogel is 20-30 mg / cm³. 3 .

[0008] Furthermore, the dielectric tangent (dielectric loss tangent) of the Co@N-PyC / MXene-BC aerogel is between 0.45 and 0.5.

[0009] This application also provides a method for preparing the above-mentioned lightweight nitrogen-doped Co-confined catalytic Co@N-PyC / MXene-BC aerogel, the preparation steps of which include:

[0010] (1) Dopamine and cobalt acetate were coated onto a Ti3C2Tx matrix by in-situ self-polymerization to obtain a composite material;

[0011] (2) Then the composite material is heat-treated to convert the dopamine in it into nitrogen-doped pyrolytic carbon, and the cobalt acetate in it is pyrolyzed into metallic cobalt particles, which are uniformly coated on the surface of the Ti3C2Tx matrix to obtain Co@N-PyC / MXene microwave absorber.

[0012] (3) Then bacterial cellulose (BC) is added to the microwave absorbing agent and mixed, and then water is added and mixed. After mixing, the lightweight Co@N-PyC / MXene-BC microwave absorbing aerogel is obtained by freeze drying.

[0013] Furthermore, the specific operation process of step (1) in-situ self-polymerization is as follows:

[0014] (1.1) The prepared few-layer Mxene Ti3C2Tx dispersion was freeze-dried to obtain Ti3C2Tx powder nanosheets;

[0015] (1.2) Prepare a Tris HCl solution with pH = 8 to 9, add dopamine powder and stir for 1 to 2 hours in the dark to obtain a uniformly dispersed dopamine solution;

[0016] (1.3) Add the powder prepared in step (1.1) to the dopamine solution in step (1.2) and stir in the dark for 2-6 hours to obtain a dispersion solution of dopamine coated on the surface of Ti3C2Tx.

[0017] (1.4) Add cobalt acetate to the dispersion solution obtained in step (1.3), continue stirring in the dark for 4-12 hours, rinse the resulting solution repeatedly with deionized water, and freeze dry to obtain the powder of the composite material.

[0018] Further, the preparation method of the few-layer Mxene Ti3C2Tx in step (1.1) is as follows: Weigh Ti3AlC2:LiF at a mass ratio of 0.8-1.2:1, then add it to a mixture of hydrochloric acid and deionized water at a volume ratio of 2.5-3.5:1, stir and react at a temperature of 40-45℃ for 24-48h, then wash repeatedly with deionized water until the solution is neutral, and sonicate the obtained solution for 2-3h to obtain a few-layer Ti3C2Tx dispersion (using few-layer Ti3C2Tx has high conductivity, and the monolayer structure makes it easy to form a conductive network).

[0019] Furthermore, in step (1.2), a 10-30 mM Tris-HCl buffer solution is prepared from tris(hydroxymethyl)aminomethane and hydrochloric acid. The purpose of this is to provide an alkaline environment for the self-polymerization of dopamine.

[0020] Furthermore, the mass ratio of the Ti3C2Tx powder nanosheets and dopamine powder added in step (1.3) is 1 to 2:1.

[0021] Furthermore, in step (1.4), the content of cobalt acetate magnetic particles loaded in the Ti3C2Tx surface-coated dopamine dispersion solution is 2-8 mg / mL.

[0022] Furthermore, the specific operation process of step (2) is as follows: the composite material obtained in step (1) is subjected to heat treatment. The heat treatment process is to place the dry powder in a tube furnace, the heat treatment temperature is 400-700℃, the heat treatment time is 1-2h, and the heat treatment process is protected by introducing Ar and H2 atmosphere.

[0023] Furthermore, the specific operation process of step (3) is as follows: add bacterial cellulose, stir and sonicate for 25-35 minutes, pour into a polytetrafluoroethylene mold, freeze-dry for 48-72 hours to obtain Co@N-PyC / MXene-BC aerogel; after the addition is completed, the proportion of the microwave absorbing agent Co@N-PyC / MXene is 1.0wt.% to 2.5wt.% of the total mass of the mixed solution of microwave absorbing agent, bacterial cellulose and water.

[0024] Furthermore, in step (3), the bacterial cellulose is a type of nanocellulose.

[0025] The advantages and beneficial effects of this application are as follows:

[0026] 1. This application discloses a lightweight Co@N-PyC / MXene-BC microwave absorbing aerogel, which has low density, high dielectric loss capability, and wide effective absorption bandwidth; the density of the Co@N-PyC / MXene-BC aerogel is 25 mg / cm³. 3 The dielectric tangent (dielectric loss tangent) of the Co@N-PyC / MXene-BC aerogel is approximately 0.48.

[0027] 2. This application employs in-situ self-polymerization to construct a multilayer dielectric loss layer on the substrate, and uses interface engineering to build multiple heterogeneous interface structures, namely pyrolytic carbon and crystalline carbon layers, metal particles and crystalline carbon layers, to promote dipole polarization and thus improve dielectric loss capability.

[0028] 3. The buffer layer introduced in this application on the Ti3C2Tx surface refers to the nitrogen-doped pyrolytic carbon layer. Since the medium dielectric loss layer can effectively neutralize the high dielectric loss layer of Ti3C2Tx, thereby improving impedance mismatch and allowing electromagnetic waves to enter the material interior as much as possible; it not only combines the abundant functional groups on the Ti3C2Tx surface, reducing the exposure of active sites and thus slowing down the oxidation of Ti3C2Tx, but also introduces a large number of defects in situ after the pyrolysis of the nitrogen-doped carbon layer formed by heat treatment. The difference between the electronegativity of pyrrole N and pyridine N and the electronegativity of the surrounding carbon atoms leads to charge redistribution and enhanced dipole polarization. The presence of graphitized N is conducive to enhancing electron migration and improving polarization and conductivity loss.

[0029] 4. This application uses a method of loading metal particles onto an amorphous carbon layer. After pyrolysis, due to the confined catalytic effect of the metal, crystalline carbon rings are precipitated around it, which promotes the movement and transition of electrons, enhances electrical conductivity loss, and improves electromagnetic wave attenuation capability.

[0030] 5. This application uses bacterial cellulose as a binder to assemble the microwave absorber into a three-dimensional macroscopic body. Although Mxene contains abundant functional groups such as -OH and -O, it is negatively charged and cannot be directly assembled into a three-dimensional aerogel. However, bacterial cellulose contains a variety of organic functional groups on its surface. The assembly of the two not only solves the problem of easy stacking of two-dimensional MXene nanosheets, but also constructs a three-dimensional macroscopic body. The construction of the conductive network provides more reflection paths for electromagnetic waves and enhances the attenuation of electromagnetic waves. The aerogel obtained by freeze-drying has a lower density and better microwave absorption performance. Attached Figure Description

[0031] Figure 1 This is a transmission electron microscope image of the Co@N-PyC / MXene microwave absorbing agent prepared in Example 1 of this application.

[0032] Figure 2 The Raman spectrum of the Co@N-PyC / MXene absorbing agent prepared in Example 1 of this application;

[0033] Figure 3 The reflection loss diagram is shown for the Co@N-PyC / MXene-BC aerogel prepared in Example 2 of this application.

[0034] Figure 4 The image shows the reflection loss of the N-PyC / MXene-BC aerogel prepared in Comparative Example 1 of this application. Detailed Implementation

[0035] The present invention will be described in further detail below with reference to specific embodiments, but the implementation of the present invention includes, but is not limited to, the scope represented by the following embodiments.

[0036] This application discloses a lightweight Co@N-PyC / MXene-BC high-loss absorbing aerogel; the aerogel uses Ti3C2Tx as a matrix, with a buffer layer and loaded cobalt particles as a dielectric loss enhancement layer on the surface, and bacterial cellulose as a binder to assemble two-dimensional nanosheets into a three-dimensional aerogel. The density of this aerogel is 25 mg / cm³. 3 This material exhibits strong loss characteristics and excellent wave absorption properties. The preparation method specifically includes the following steps:

[0037] Example 1:

[0038] (1) Weigh Ti3AlC2:LiF at a mass ratio of 1:1, then add it to a mixture of hydrochloric acid and deionized water at a volume ratio of 3:1. Stir the mixture at 40-45℃ for 24-48 hours, then wash it repeatedly with deionized water until the solution is neutral. Sonicate the resulting solution for 2-3 hours to obtain a few-layer Ti3C2Tx dispersion (few-layer Ti3C2Tx has high conductivity, and its monolayer structure easily forms a conductive network); then freeze-dry the prepared few-layer Mxene Ti3C2Tx dispersion to obtain Ti3C2Tx powder nanosheets; prepare a pH=8.5, 15mM Tris buffer solution, magnetically stirred for 30 min, weighed 0.2 g of dopamine powder and added to the buffer solution, stirred at room temperature in the dark for 2 h; weighed the same mass of Ti3C2Tx powder nanosheets and added, then sonicated for 30 min to ensure that the nanosheets are evenly distributed in the solution, stirred in the dark for 4 h to obtain a Ti3C2Tx surface coated with polydopamine mixed solution.

[0039] (2) The obtained mixed solution was cleaned with deionized water and ethanol by vacuum filtration, and the dopamine coating process in step (1) was repeated. Then, 4 mg / mL cobalt acetate particles were added and stirred in the dark for 4 h. A mixture of metal particles and polydopamine-coated Ti3C2Tx was obtained. The mixture was repeatedly cleaned with deionized water and dried by freeze drying for 48 h to obtain a powder.

[0040] (3) The obtained mixture powder was placed in an atmosphere-protected heat treatment furnace for heat treatment. The gas introduced during the heat treatment process was a hydrogen / argon mixture with a hydrogen content of 20%, a gas flow rate of 20 ml / min, a heating rate of 5℃ / min, a heat treatment temperature of 600℃, and a heat treatment time of 1 h, to obtain Co@N-PyC / MXene microwave absorber.

[0041] (4) The microwave absorbing agent obtained in step (3) is mixed with bacterial cellulose at a mass ratio of 5:1. Then it is mixed and stirred with deionized water. After mixing and stirring, the mass fraction of microwave absorbing agent in the total mixture is 2.5 wt.% and the mass fraction of BC is 0.5 wt.%. The mixture is sonicated for 15 min. The resulting mixed solution is poured into a polytetrafluoroethylene mold and then frozen, demolded, and dried for 48 h to obtain Co@N-PyC / MXene-BC microwave absorbing aerogel.

[0042] (5) The electromagnetic parameters of Co@N-PyC / MXene-BC absorbing aerogel were tested using the waveguide method, and the corresponding reflection loss was calculated. The results are shown in the attached table. Figure 2 middle.

[0043] Figure 1The image shows a transmission electron microscope (TEM) image of the Co@N-PyC / MXene microwave absorber in Example 1. It can be seen that crystalline carbon rings appear on the pyrolytic carbon layer on the Ti3C2Tx matrix. This is because the catalytic effect of the cobalt particles transforms the amorphous carbon around the cobalt particles into crystalline carbon.

[0044] Figure 2 The Raman spectrum of the Co@N-PyC / MXene absorbing agent in Example 1 shows the typical D and G peaks of carbon materials, and the I peak of Co@N-PyC / Ti3C2Tx. D / I G The ratio of 1.6 indicates that the degree of crystallization is high after Ti3C2Tx is coated with pyrolytic carbon and after Co particles are loaded.

[0045] Example 2:

[0046] (1) Weigh Ti3AlC2:LiF at a mass ratio of 1:1, then add it to a mixture of hydrochloric acid and deionized water at a volume ratio of 3:1. Stir the mixture at 40-45℃ for 24-48 hours, then wash it repeatedly with deionized water until the solution is neutral. Sonicate the resulting solution for 2-3 hours to obtain a few-layer Ti3C2Tx dispersion (few-layer Ti3C2Tx has high conductivity, and its monolayer structure easily forms a conductive network); then freeze-dry the prepared few-layer Mxene Ti3C2Tx dispersion to obtain Ti3C2Tx powder nanosheets; prepare a pH=8.5, 15mM In a Tris buffer solution, the mixture was magnetically stirred for 30 min. 0.2 g of dopamine powder was weighed and added to the buffer solution, and stirred at room temperature in the dark for 2 h. The same mass of Ti3C2Tx powder was weighed and added to the dispersion, and sonicated for 30 min to ensure uniform distribution of the nanosheets in the solution. The mixture was stirred in the dark for 4 h to obtain a Ti3C2Tx surface-coated polydopamine mixed solution. The obtained mixed solution was then cleaned with deionized water and ethanol using vacuum filtration.

[0047] (2) Then add 8 mg / mL cobalt acetate particles and stir in the dark for 4 h; obtain a mixture of metal particles and polydopamine-coated Ti3C2Tx, wash it repeatedly with deionized water, and dry it by freeze drying for 48 h to obtain a mixture powder;

[0048] (3) The obtained powder was placed in an atmosphere-protected heat treatment furnace for heat treatment. The gas introduced was a hydrogen / argon mixture with a hydrogen content of 20%, a flow rate of 20 ml / min, a heating rate of 5℃ / min, a heat treatment temperature of 600℃, and a heat treatment time of 1 h to obtain Co@N-PyC / MXene microwave absorber.

[0049] (4) The microwave absorbing agent obtained in step (3) is mixed with bacterial cellulose at a mass ratio of 5:1, and then mixed with deionized water. The total mass fraction of microwave absorbing agent in the mixture is 2.5 wt.% and the mass fraction of BC is 0.5 wt.%. The mixture is sonicated for 15 min, and the resulting mixed solution is poured into a polytetrafluoroethylene mold. After freezing, demolding and drying for 48 h, Co@N-PyC / MXene-BC microwave absorbing aerogel is obtained.

[0050] Figure 3 The Co@N-PyC / MXene-BC absorbing aerogel in Example 2 exhibits the following reflection loss capability: frequency 10.1dB, thickness 3.0mm, minimum reflection loss of -66.0dB, and effective absorption bandwidth of up to 3.8dB in the X-band.

[0051] Comparative example: 1N-PyC / Mxene aerogel

[0052] To demonstrate the effect of metal particles on the dielectric properties of aerogels, this application includes a comparative example without metal particles. N-PyC / Mxene aerogels were prepared using the method of Example 1 (excluding step (2)). The electromagnetic parameters of the aerogels were tested using the waveguide method, and their corresponding reflection losses were calculated. The results are presented as an appendix. Figure 4 As shown in the figure, the thickness is 3.1 mm, the frequency is 11.4 GHz, and the minimum RL value is -20.5 dB. The dielectric loss capability is relatively weak, which is not conducive to meeting the impedance matching requirements and results in weak absorption performance. This indicates that the polarization and conductivity loss capabilities are insufficient when no metal particles are loaded, leading to a decrease in absorption performance.

Claims

1. A lightweight Co@N-PyC / MXene-BC microwave absorbing aerogel, characterized in that: The material includes: a Ti3C2Tx nanosheet matrix, on which a pyrolytic carbon layer and cobalt particles are coated, and bacterial cellulose is added to assemble a Co@N-PyC / MXene-BC aerogel; the preparation steps of the aerogel include: (1) coating dopamine and cobalt acetate on the Ti3C2Tx matrix by in-situ self-polymerization to obtain a composite material; (2) then heat-treating the composite material to convert the dopamine in it into nitrogen-doped pyrolytic carbon, and pyrolyzing the cobalt acetate in it into cobalt particles, which are uniformly coated on the surface of the Ti3C2Tx matrix to obtain a Co@N-PyC / MXene microwave absorber; (3) then adding bacterial cellulose to the microwave absorber and mixing, then adding water and stirring, and then freeze-drying to obtain a lightweight Co@N-PyC / MXene-BC microwave absorbing aerogel.

2. The lightweight Co@N-PyC / MXene-BC microwave absorbing aerogel according to claim 1, characterized in that: The density of the Co@N-PyC / MXene-BC aerogel is 20-30 mg / cm³. 3 .

3. The lightweight Co@N-PyC / MXene-BC microwave absorbing aerogel according to claim 1, characterized in that: The dielectric tangent of the Co@N-PyC / MXene-BC aerogel is 0.45-0.

5.

4. The lightweight Co@N-PyC / MXene-BC microwave absorbing aerogel according to claim 1, characterized in that: The in-situ self-polymerization of step (1) is specifically carried out as follows: (1.1) The prepared few-layer Mxene Ti3C2Tx dispersion is freeze-dried to obtain Ti3C2Tx powder nanosheets; (1.2) A Tris HCl solution with pH = 8-9 is prepared, and dopamine powder is added and stirred in the dark for 1-2 hours to obtain a uniformly dispersed dopamine solution; (1.3) The powder prepared in step (1.1) is added to the dopamine solution in step (1.2) and stirred in the dark for 2-6 hours to obtain a dispersion solution with dopamine coated on the surface of Ti3C2Tx; (1.4) Cobalt acetate is added to the dispersion solution obtained in step (1.3) and stirred in the dark for 4-12 hours. The obtained solution is repeatedly rinsed with deionized water and freeze-dried to obtain the powder of the composite material.

5. The lightweight Co@N-PyC / MXene-BC microwave absorbing aerogel according to claim 4, characterized in that: The preparation method of few-layer Mxene Ti3C2Tx in step (1.1) is as follows: Weigh Ti3AlC2:LiF at a mass ratio of 0.8-1.2:1, then add it to a mixture of hydrochloric acid and deionized water at a volume ratio of 2.5-3.5:1, stir and react at a temperature of 40-45℃ for 24-48h, then wash repeatedly with deionized water until the solution is neutral, and sonicate the obtained solution for 2-3h to obtain a few-layer Ti3C2Tx dispersion.

6. The lightweight Co@N-PyC / MXene-BC microwave absorbing aerogel according to claim 4, characterized in that: In step (1.2), a 10-30 mM Tris-HCl buffer solution is prepared using tris(hydroxymethyl)aminomethane and hydrochloric acid.

7. The lightweight Co@N-PyC / MXene-BC microwave absorbing aerogel according to claim 4, characterized in that: The mass ratio of the Ti3C2Tx powder nanosheets and dopamine powder added in step (1.3) is 1 to 2:

1.

8. The lightweight Co@N-PyC / MXene-BC microwave absorbing aerogel according to claim 4, characterized in that: The content of cobalt acetate magnetic particles in the Ti3C2Tx surface-coated dopamine dispersion solution described in step (1.4) is 2-8 mg / mL.

9. The lightweight Co@N-PyC / MXene-BC microwave absorbing aerogel according to claim 1, characterized in that: The specific operation process of step (2) is as follows: the composite material obtained in step (1) is subjected to heat treatment. The heat treatment process is to place the dry powder in a tube furnace, the heat treatment temperature is 400-700℃, the heat treatment time is 1-2h, and Ar and H2 atmospheres are introduced for protection during the heat treatment process.

10. The lightweight Co@N-PyC / MXene-BC microwave absorbing aerogel according to claim 1, characterized in that: The specific operation process of step (3) is as follows: add bacterial cellulose, stir and sonicate for 25-35 min, pour into a polytetrafluoroethylene mold, freeze-dry for 48-72 h to obtain Co@N-PyC / MXene-BC aerogel; after the addition is completed, the proportion of the microwave absorbing agent Co@N-PyC / MXene is 1.0 wt.% to 2.5 wt.% of the total mass of the mixed solution of microwave absorbing agent, bacterial cellulose and water.

11. The lightweight Co@N-PyC / MXene-BC microwave absorbing aerogel according to claim 1, characterized in that: In step (3), bacterial cellulose is a type of nanocellulose.

Images