Transition metal doped three-dimensional TiN-coated CNTs wave-absorbing material as well as preparation method and application thereof

Abstract

The invention discloses a transition metal doped three-dimensional TiN-coated CNTs wave-absorbing material as well as a preparation method and application thereof, and belongs to the field of wave-absorbing materials. The preparation method comprises the following steps: adding a transition metal salt solution into an MXene dispersion liquid, and freeze-drying to obtain activated MXene powder; and uniformly mixing the transition metal-doped three-dimensional TiN-coated CNTs with a carbon-containing nitrogen compound, calcining in an inert gas atmosphere, and cooling to room temperature to obtain the transition metal-doped three-dimensional TiN-coated CNTs material. The prepared wave-absorbing material is excellent in impedance matching degree, good in chemical stability and not prone to being oxidized, and the excellent wave-absorbing performance can be achieved under the condition that the adding amount is lower than 5 wt%.

Description

Technical Field

[0001] This invention relates to the field of composite materials technology, specifically to a method for preparing and applying a transition metal-doped three-dimensional TiN@CNTs microwave absorbing material. Background Technology

[0002] With the rapid development of electronic technology, electromagnetic radiation pollution has become an increasingly prominent problem. Microwave absorbing materials can effectively convert microwave energy into heat and other forms of energy through mechanisms such as polarization, resonance, and conduction, and then dissipate them. However, traditional microwave absorbing materials (such as metals, magnetic oxides, and ceramics) rely solely on a single loss mechanism, resulting in narrow effective bandwidths and requiring excessive amounts, making it difficult to meet practical application needs. Therefore, developing efficient, wideband, and ultrathin microwave absorbing materials has become an important research topic in materials science.

[0003] Currently, commonly used two-dimensional nanomaterials like MXene, with their high specific surface area, tunable surface functional groups, and metal-like conductivity, have become high-performance microwave absorbers through interfacial polarization and multiple reflection effects. However, monolayer MXene suffers from a severe imbalance between its dielectric constant and magnetic permeability due to the lack of intrinsic magnetic permeability loss, resulting in a large amount of electromagnetic waves being reflected from its surface and not effectively absorbed. Furthermore, the environmental sensitivity of MXene (conductivity decreases by 38% when humidity > 60%) still limits its engineering applications. To address these shortcomings, one approach is to attempt an in-situ topological transformation of monolayer MXene into TiN to improve its chemical stability. Simultaneously, introducing magnetic materials into the system can achieve impedance matching in the composite material, thereby enhancing its microwave absorption performance. Summary of the Invention

[0004] To achieve the above objectives, this invention discloses a method for preparing a transition metal-doped three-dimensional multifunctional TiN@CNTs heterostructure material, comprising the following steps:

[0005] The first step involves adding an appropriate amount of transition metal ion salt solution to the MXene solution at room temperature, followed by freeze-drying to obtain metal ion-activated MXene powder.

[0006] The second step involves mixing the powder sample obtained in the first step with a carbon-nitrogen compound, grinding it thoroughly and uniformly, calcining it in an inert gas atmosphere, and cooling it to room temperature to obtain transition metal-doped TiN nanosheets with abundant CNTs on the surface.

[0007] Preferably, the concentration of the MXene solution is 1-20 mg / ml, and the solvent is one or two of deionized water, benzene, toluene, N,N-dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, methanol, ethanol, and acetone.

[0008] Preferably, the metal ion salt solution is one of the chloride, nitrate, acetate, sulfate and hydrate of iron, cobalt and nickel ions, with a concentration of 0.3-1.0 mol / L and a volume ratio of 1:20 with the MXene solution.

[0009] Preferably, the carbon-nitrogen-containing compound is at least one of urea, cyanamide, dicyandiamide, melamine, triethylamine, and p-nitroaniline containing carbon-nitrogen molecules, in a mass ratio of 1:5-20;

[0010] Preferably, the inert gas atmosphere is nitrogen, the maximum calcination temperature is 400-1000 °C, the holding time is 0.5-4 h, and the heating rate is 5 °C / min;

[0011] This invention provides an application of transition metal-doped three-dimensional multifunctional TiN@CNTs heterostructure material in the 2-18 GHz electromagnetic band.

[0012] This invention addresses the shortcomings of the prior art and offers the following advantages: MXene is mixed with metal ions and carbon-nitrogen compounds, followed by high-temperature annealing. Utilizing topological chemistry and vapor-phase thermal deposition, the two-dimensional MXene is topologically converted into a transition metal-doped TiN structure at high temperature. The carbon-nitrogen compounds, acting as a carbon source, are grown into CNTs under the catalysis of metal particles. In this invention, transition metal-doped TiN and metal-terminated CNTs successfully combine to construct a heterojunction structure, establishing excellent adjustable impedance matching characteristics and a rich microwave absorption matrix. The magnetic metal, with its good dispersion, achieves high-efficiency magnetic loss, promoting electromagnetic wave attenuation. The CNTs and metal-doped TiN, with their good conductivity, increase the material's conductive loss. Furthermore, significant dipole polarization exists between transition metal-doped TiN and CNTs, and between CNTs and the magnetic metal. These multiple loss mechanisms synergistically achieve the high-efficiency microwave absorption performance of the transition metal-doped TiN@CNTs heterostructure material. The heterostructure material prepared by this invention exhibits excellent impedance matching performance, with a maximum reflection loss reaching -58.17 dB. With an absorber thickness of 2.0 mm, the bandwidth with a reflection loss of less than -10 dB can reach 5.31 GHz, ranging from 12.69 to 18 GHz. Attached Figure Description

[0013] Figure 1 This is a scanning electron microscope image of the Co-doped TiN@CNTs obtained in Example 1; Figure 2 This is a scanning electron microscope image of the Fe-doped TiN@CNTs obtained in Example 2; Figure 3 This is a transmission electron microscope (TEM) image of the Ni-doped TiN@CNTs obtained in Example 3; Figure 4 The image shows a transmission electron microscope (TEM) image of the Co-doped TiN@CNTs obtained in Example 1. Figure 5 The image shows a transmission electron microscope (TEM) image of the Co-doped TiN@CNTs obtained in Example 1. Figure 6 The images show the XRD patterns of Co-doped TiN@CNTs obtained at different temperatures in Examples 4-7. Figure 7 The Raman spectra of the materials obtained in Examples 4-7 at temperatures of 700 °C and 750 °C are shown. Figure 8 This is a comparison of the shape of the aerogel prepared after adding the polymer chitosan in Example 8 before and after retraction.

[0021] Figure 9 The graph shows the reflection loss (RL) and frequency (f) of the composite material obtained in Example 1. Detailed Implementation

[0022] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way. Unless otherwise specified, the test methods described in the following embodiments are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0023] Example 1

[0024] A method for preparing three-dimensional TiN@CNTs doped with transition metals, the experimental steps of which are as follows:

[0025] The first step involves adding a 0.5 mol / L cobalt chloride solution to a 5 mg / ml MXene solution at room temperature, with a volume ratio of 1:20. After freeze-drying, metal ion-activated MXene powder is obtained.

[0026] In the second step, the powder sample obtained in the first step was mixed with melamine at a mass ratio of 1:10, ground thoroughly and uniformly, and then calcined in a tube furnace under a nitrogen atmosphere. The maximum annealing temperature was 750 °C, maintained for 2 h, and then cooled to room temperature to obtain Co-doped TiN nanosheets with abundant CNTs on the surface.

[0027] It was mixed with paraffin at a mass ratio of 5:95 to prepare concentric ring samples for testing.

[0028] Example 2-3

[0029] The cobalt chloride solution was replaced with ferric chloride solution and nickel chloride solution respectively, while keeping other conditions the same, to obtain the corresponding microwave absorbing materials.

[0030] Examples 4-7

[0031] The maximum annealing temperature of the powder was changed to 400 °C, 500 °C, 600 °C, and 700 °C respectively, while keeping other conditions the same, to obtain the corresponding microwave absorbing materials.

[0032] Examples 8-12

[0033] The first step involves adding a 0.5 mol / L cobalt chloride solution to a 5 mg / ml MXene solution at a volume ratio of 1:20. Then, an aqueous solution of one of the following—chitosan, polyvinyl alcohol, sodium alginate, cellulose nanofibers, or bacterial cellulose—at a volume ratio of 1 wt% is added. After freeze-drying, an aerogel is obtained.

[0034] The second step involves placing the aerogel obtained in the first step into a tube furnace under a nitrogen atmosphere for calcination. The maximum annealing temperature is 750 °C, which is maintained for 2 hours. After cooling to room temperature, the corresponding microwave absorbing material is obtained.

[0035] The morphology of different metal-doped microwave absorbing materials was observed using scanning electron microscopy. For example... Figure 1-3 As shown, MXene activated by different metal ions can be topologically transformed into transition metal-doped TiN sheets at high temperatures, and CNTs structures with an inner diameter of 15 nm are grown in situ on the surface. The CNTs are uniformly dispersed without obvious entanglement, which can effectively improve the impedance matching performance of the material.

[0036] Further analysis of different components in the cobalt-doped microwave absorbing material was conducted using transmission electron microscopy. For example... Figure 4-5 As shown, the lattice spacings of 0.215, 0.24, 0.21 and 0.34 nm are attributed to the Co (111), TiN (111), CoN and graphitic carbon (002) planes, respectively.

[0037] Taking a cobalt-doped sample as an example, X-ray diffraction patterns are used to analyze the absorbing material. Figure 6 As shown, comparing the heterostructure products obtained at different temperatures, it can be seen that melamine gradually decomposes to form g-C3N4 in the 400-600 °C range (complete conversion at 600 °C). At 700 °C, the system shows TiN diffraction peaks (6.6°, 42.6°, 61.8°) and cobalt ions begin to be reduced, but the graphitic carbon peak (26.5°) is missing. Figure 7The Raman spectra of the products at 700 °C and 750 °C show that the material obtained at 750 °C has I D / I G The value was significantly higher than that of the product obtained at 700 °C (0.91), indicating that cobalt had not yet fully activated carbon structure recombination at this stage. When the temperature was raised to 750 °C and held at that temperature for 2 h, the catalytic activity of metallic cobalt was significantly enhanced, driving the directional epitaxial growth of free carbon to form a highly graphitized CNT network, while the two-dimensional structure of TiN was completely preserved.

[0038] Figure 8 The image shows a comparison of the aerogel shapes before and after annealing with chitosan in Example 8. The image shows that when at least one polymer is added to the system to form an aerogel, the volume of the material shrinks drastically before and after annealing; the internal structure collapses, the material becomes brittle, and subsequent experiments cannot be completed. The fundamental reason for this phenomenon is that the molecular skeleton of natural polymers is mainly composed of carbon, hydrogen, and oxygen. Under high-temperature conditions of 750 °C, these polymers undergo significant thermal decomposition reactions, accompanied by the breaking of chemical bonds such as CH, CO, and CC, producing and releasing volatile small molecule products including H2O, CO, CO2, CH4, and various aldehydes and carboxylic acids. This process leads to a significant loss of solid components in the three-dimensional network skeleton of the aerogel. In the inert atmosphere provided by N2 protection, the remaining carbon atoms further rearrange to form a turbulent layered graphite-like structure, resulting in a significant increase in the overall density of the material, macroscopically manifested as a sharp volume shrinkage. On the other hand, the removal of H and O elements destroys the original cross-linking structures such as hydrogen bonds and ether bonds. In addition, the porosity and defects introduced by the escape of volatile components lead to a significant decrease in the mechanical properties of the material after heat treatment.

[0039] Meanwhile, the MXene component introduced into the aerogel itself lacks self-supporting mechanical properties; its structural integrity relies on the polymer to bridge and fix the layers. During high-temperature annealing, both the polymer binder phase and MXene decompose and undergo structural evolution, causing the material layers to lose support, the overall network to collapse, and mechanical properties to be lost, failing to meet the requirements of subsequent experiments. On the other hand, if the proportion of polymer added during preparation is too low, the aerogel may also have low initial mechanical properties before annealing due to insufficient crosslinking density or phase separation, which is also detrimental to experimental operation and material stability. Therefore, using polymers as a bonding and auxiliary molding strategy is neither applicable nor feasible in this material system.

[0040] Figure 9The image shows a 2D reflection loss diagram of the cobalt-doped TiN@CNTs heterostructure prepared in Example 1, with frequencies ranging from 2.0 to 18.0 GHz and thicknesses from 1.0 to 5.0 mm. The diagram shows that the material exhibits a maximum reflection loss of -58.17 dB at 5.50 GHz; and within the thickness range of 1.0–5.0 mm, the frequency band with a reflection loss less than -10 dB is 12.69–18 GHz, covering 93.6% of the Ku band, indicating that the absorbing material possesses excellent electromagnetic wave absorption capabilities.

[0041] Examples 13-20

[0042] The solvent in the MXene solution was changed to one of benzene, toluene, N,N-dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, methanol, ethanol, or acetone, while other conditions remained the same as in Example 1, to obtain the corresponding heterojunction material.

[0043] Examples 21-24

[0044] The concentration of the cobalt chloride solution was changed to 0.3, 0.4, 0.6, and 0.7 mol / L, while other conditions remained the same as in Example 1, to obtain the corresponding heterojunction materials.

[0045] Examples 25-29

[0046] By replacing the carbon-nitrogen compound with at least one of urea, cyanamide, dicyandiamide, triethylamine, and p-nitroaniline, and keeping other conditions the same as in Example 1, the corresponding heterojunction material was obtained.

[0047] Examples 30-31

[0048] By changing the inert gas atmosphere to either argon or helium, and keeping other conditions the same as in Example 1, the corresponding heterojunction material was obtained.

[0049] The above embodiments are only used to illustrate the present invention. Any equivalent transformations and improvements made on the basis of the technical solutions of the present invention should not be excluded from the protection scope of the present invention.

Claims

1. A method for preparing transition metal-doped three-dimensional TiN@CNTs microwave absorbing materials, characterized in that, Includes the following steps: S1. At room temperature, a transition metal salt solution is added to the MXene solution, and after freeze-drying, metal ion-activated MXene powder is obtained. S2. The MXene powder activated by the metal ions is thoroughly ground with carbon and nitrogen compounds, calcined in an inert atmosphere, and cooled to room temperature to obtain transition metal-doped titanium nitride nanosheets with abundant carbon nanotubes on the surface.

2. The preparation method according to claim 1, characterized in that, The concentration of the MXene solution is 1-20 mg / ml, and the solvent is one or two of deionized water, benzene, toluene, N,N-dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, methanol, ethanol, and acetone.

3. The preparation method according to claim 1, characterized in that, The transition metal salt is one of the chloride, nitrate, acetate, sulfate, and hydrate salts of iron, cobalt, and nickel ions.

4. The preparation method according to claim 1, characterized in that, The concentration of the metal salt solution is 0.3-1.0 mol / L, and its volume ratio with the MXene solution is 1:

20.

5. The preparation method according to claim 1, characterized in that, The carbon-nitrogen compound is at least one of urea, cyanamide, dicyandiamide, melamine, triethylamine, and p-nitroaniline molecules, and the mass ratio of the metal ion-activated MXene powder to the carbon-nitrogen compound is 1:5-20.

6. The preparation method according to claim 1, characterized in that, The inert atmosphere is provided by at least one of nitrogen, argon, and helium, and the carrier gas flow rate is 0.1-5.0 L / h.

7. The preparation method according to claim 1, characterized in that, The maximum calcination temperature is 400-1000℃, the holding time is 0.5-4 h, and the heating rate is 5℃ / min.

8. A microwave absorbing material, characterized in that: The microwave absorbing material is prepared by any one of the preparation methods described in claims 1-7.

9. The application of the microwave absorbing material according to claim 8 in electromagnetic wave absorption.

Images