Preparation method and application of high-performance carbon wave-absorbing material with controllable morphology

Abstract

The application relates to a preparation method and application of a high-performance carbon wave-absorbing material with controllable morphology, and belongs to the technical field of wave-absorbing materials.The application aims to solve the technical problems of imbalance between impedance matching characteristics and attenuation characteristics of a pure carbon absorbent and limited effective absorption frequency band.The method comprises the following steps: firstly, under heating conditions, melamine and cyanuric acid are respectively dissolved in deionized water or an ethanol aqueous solution; then, the melamine solution is added dropwise into the cyanuric acid solution, heated and stirred to react, so that a hydrogen-bonded organic framework is obtained; and then, the hydrogen-bonded organic framework is added into a phenolic resin anhydrous ethanol solution, stirred to react, and calcined, so that the carbon wave-absorbing material is obtained.The method is simple in process and low in cost.The obtained wave-absorbing material has excellent electromagnetic wave absorption performance and almost covers the whole X and Ku wave bands, so that the application requirements of thinness, lightness, wide frequency band and high strength are realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of wave-absorbing materials, and particularly relates to a preparation method and application of a high-performance carbon wave-absorbing material with controllable morphology. BACKGROUND

[0002] Microwave technology represented by 5G has developed rapidly and is widely used in many fields such as national defense and military, electronic communication, medical treatment and the like. The thermal effect, non-thermal effect and long-term cumulative effect of electromagnetic waves pose a serious threat to human health, the operation of precision equipment, and even national security and information protection. Therefore, it is urgent to design and develop light, thin and efficient electromagnetic wave absorbing materials to cope with these challenges.

[0003] Carbon materials have the advantages of low density, high tunability, good chemical stability and diversified preparation methods, and are excellent wave-absorbing materials. However, due to the intrinsic high electrical conductivity and simple structure and morphology of common carbon materials such as carbon black, graphite and graphene, it is difficult to achieve a balance between impedance matching characteristics and attenuation characteristics. Due to the skin effect, the incident electromagnetic wave is easily reflected back to the free space on the surface of these materials, so they are difficult to achieve high-efficiency absorption in a wide frequency range. In order to solve the above problems, some researchers have constructed carbon-based absorbers with different morphologies by means of template method to reduce the wave impedance of the absorber body, such as one-dimensional carbon nanotubes, two-dimensional carbon nanosheets and three-dimensional porous carbon. However, the electromagnetic loss introduced by single shape geometry is still limited and is not enough to significantly broaden the absorption bandwidth of carbon-based absorbers. At the same time, the template addition and removal involved in the template method are not conducive to the simplification of the preparation process and the control of the manufacturing cost, which limits the practical application potential of these absorbers. SUMMARY

[0004] The purpose of the present application is to solve the technical problems of the imbalance between impedance matching characteristics and attenuation characteristics and the limited effective absorption frequency band of the existing pure carbon absorber, and to provide a preparation method and application of a high-performance carbon wave-absorbing material with controllable morphology.

[0005] One of the purposes of the present application is to provide a preparation method of a high-performance carbon wave-absorbing material with controllable morphology, which is carried out according to the following steps:

[0006] S1: under heating conditions, melamine and cyanuric acid are respectively dissolved in deionized water or respectively dissolved in an ethanol aqueous solution, then the melamine solution is added dropwise into the cyanuric acid solution, heated and stirred for reaction, after the reaction is completed, the hydrogen-bonded organic framework is obtained by washing with hot water through suction filtration and freeze-drying;

[0007] S2: hydrogen-bonded organic framework is added to the phenolic resin anhydrous ethanol solution, stirring reaction, after centrifugation, the solid product is dried, calcined under protective atmosphere, to obtain carbon wave absorbing material.

[0008] Further limited, the mass ratio of melamine and cyanuric acid in S1 is 1.5:(1-2).

[0009] Further limited, the concentration of ethanol in the aqueous ethanol solution in S1 is 40-60vol%.

[0010] Further limited, the concentration of melamine solution in S1 is 0.01-0.02g / mL.

[0011] Further limited, the concentration of cyanuric acid solution in S1 is 0.01-0.02g / mL.

[0012] Further limited, the temperature of heating stirring reaction in S1 is 70-90℃, and the time is 1-3h.

[0013] Further limited, the 70-90℃ hot water cleaning in S1.

[0014] Further limited, the mass ratio of hydrogen-bonded organic framework and phenolic resin in S2 is 0.5:(0.3-0.5).

[0015] Further limited, the concentration of phenolic resin in the anhydrous ethanol solution of phenolic resin in S2 is 6-10mg / mL.

[0016] Further limited, the stirring reaction time in S2 is 10-12h.

[0017] Further limited, the drying temperature in S2 is 50-70℃.

[0018] Further limited, the calcination procedure in S2: first, increase the temperature to 350-450℃ at the rate of 1-3℃ / min, and keep the temperature for 1-2.5h, then increase the temperature to 500-550℃, keep the temperature for 2-4h, continue to increase the temperature to 700-800℃, keep the temperature for 1.5-4h, and then cool down to room temperature.

[0019] The second object of the present application is to provide a one-dimensional tubular carbon wave absorbing material prepared by the above method, which is dissolved in deionized water to obtain a one-dimensional tubular carbon wave absorbing material with a length of 3-5μm, a tube diameter of 200-400nm, and a wall thickness of <10nm.

[0020] The third object of the present application is to provide a three-dimensional network carbon wave absorbing material prepared by the above method, which is dissolved in an aqueous ethanol solution to obtain a three-dimensional network carbon wave absorbing material with a size of 10-40μm and micron and sub-micron pores.

[0021] The fourth object of the present application is to provide a one-dimensional tubular carbon wave-absorbing material and a three-dimensional network carbon wave-absorbing material in a thickness range of 1-5 mm for absorbing electromagnetic waves in a frequency range of 2-18 GHz.

[0022] The fifth object of the present application is to provide a wave-absorbing coating prepared from the one-dimensional tubular carbon wave-absorbing material and the three-dimensional network carbon wave-absorbing material.

[0023] Compared with the prior art, the present application has the following remarkable effects:

[0024] The present application provides two kinds of high-performance pure carbon wave-absorbing materials with controllable morphology and a preparation method thereof. The method first utilizes hydrogen bond self-assembly between melamine and cyanuric acid to obtain a hydrogen-bond organic framework material, and further coats a layer of low-order phenolic resin molecules on the surface of the hydrogen-bond organic framework material as a carbon source through secondary hydrogen bond action. In this process, the morphology of the prepared hydrogen-bond organic framework material can be effectively controlled by changing the liquid phase environment of hydrogen bond self-assembly. In the heat treatment process, the melamine-cyanuric acid hydrogen-bond organic framework material undergoes polycondensation reaction to first generate a nitrogenated carbon phase composed of triazine rings. As the heat treatment temperature increases, the thermally unstable triazine rings begin to decompose to generate N-containing gaseous carbon, part of which overflows from the pores in the inner cavity of the material, and part of which is doped into the carbon matrix derived from the phenolic resin molecules, finally forming a unique porous hollow structure. Finally, as the heat treatment temperature continuously increases, the carbon atoms in the carbon matrix partially rearrange in an orderly manner to gradually generate short-range ordered carbon nanocrystals, thereby improving the electronic transport capability. The innovations of the present application are as follows:

[0025] (1) The present application realizes controllable adjustment of the morphology by hydrogen bond self-assembly between melamine and cyanuric acid and secondary hydrogen bond coating, and through simple reaction solvent control. After carbonization, one-dimensional tubular Mtube and three-dimensional network Mfoam absorbers are constructed. The process is simple and the cost is low.

[0026] (2) The one-dimensional tubular Mtube and three-dimensional network Mfoam absorbers prepared by the present application have a large pore structure, which is beneficial to improving the impedance matching characteristics of the material; the order degree of carbon atoms is low, and there are abundant carbon nanocrystals, N-doped atoms and vacancy defects in the structure, which can effectively control the electrical conductivity of the material in a suitable range while inducing strong polarization relaxation loss. By utilizing the coupling effect between N atom doping, carbon nanocrystal introduction and shape geometric effect, the absorber exhibits the maximum cooperation between resistance loss, polarization relaxation behavior and impedance matching, and realizes the application requirements of "thin, light, wide and strong".

[0027] (3) The one-dimensional tubular Mtube and three-dimensional network Mfoam absorbers prepared by the present application have excellent electromagnetic wave absorption performance. Benefiting from the synergistic effect among multiple polarization relaxation behaviors, resistance loss and impedance matching, the minimum reflection loss of the two reaches -55.32 dB and -26.49, respectively, and the effective absorption bandwidths of ≤-10 dB (90% absorption rate) reach 8.52 GHz at a thickness of 2.64 mm and 7.88 GHz at a thickness of 2.42 mm, respectively, covering almost all X and Ku bands. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 Scanning electron microscope (SEM) images, high-angle annular dark field scanning transmission electron microscope (HAADF-STEM) images and high-resolution transmission electron microscope (HRTEM) images of the one-dimensional tubular Mtube and three-dimensional network Mfoam wave-absorbing materials prepared in Examples 1-2; (a)-Mtube-SEM, (c)-Mtube-HAADF-STEM, (b)-Mfoam-SEM, (d)-Mfoam-HAADF-STEM, (e)-Mtube-HRTEM, (f)-Mfoam-HRTEM;

[0029] Figure 2 X-ray diffraction (XRD) patterns and Fourier transform infrared absorption spectra (FTIR) of the one-dimensional tubular Mtube and three-dimensional network Mfoam wave-absorbing materials prepared in Examples 1-2; (a)-XRD, (b)-FTIR;

[0030] Figure 3 Ultraviolet excitation Raman spectra (uv-Raman) of the one-dimensional tubular Mtube and three-dimensional network Mfoam wave-absorbing materials prepared in Examples 1-2;

[0031] Figure 4 Dielectric constant curves of the one-dimensional tubular Mtube and three-dimensional network Mfoam wave-absorbing materials prepared in Examples 1-2; (a)-real part, (b)-imaginary part;

[0032] Figure 5 Comprehensive wave-absorbing performance of the one-dimensional tubular Mtube and three-dimensional network Mfoam wave-absorbing materials prepared in Examples 1-2; (a)-Example 1, (b)-Example 2;

[0033] Figure 6 Wave-absorbing performance curves of the one-dimensional tubular Mtube and three-dimensional network Mfoam wave-absorbing materials prepared in Examples 1-2 at different thicknesses. DETAILED DESCRIPTION

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0035] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0036] The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used in the following embodiments, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such a composition, step, method, article, or apparatus.

[0037] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0038] Example 1:

[0039] The preparation method of the one-dimensional tubular carbon microwave absorbing material in this embodiment is carried out according to the following steps:

[0040] (1) Add 1.50 g of melamine to 100 mL of deionized water and stir at 80 °C until completely dissolved to obtain a melamine solution. Add 1.52 g of cyanuric acid to 100 mL of deionized water and stir at 80 °C until completely dissolved to obtain a cyanuric acid solution. Add the obtained melamine solution dropwise to the obtained cyanuric acid solution and stir at 80 °C for 2 h. Transfer the product to a vacuum filtration flask, wash with 80 °C hot water, and freeze-dry for 48 h to obtain a hydrogen-bonded organic framework material.

[0041] (2) Take 0.5 g of the hydrogen-bonded organic framework product and add it to 50 mL of a phenol-formaldehyde resin (molecular weight 1000) anhydrous ethanol solution with a concentration of 0.008 g / mL. After stirring for 12 h, centrifugation is performed to obtain a solid product, which is dried at 60°C, then placed in a sealed porcelain boat, and calcined in a tube furnace under an argon atmosphere. First, heating is performed at a rate of 2°C / min to 400°C and held for 2 h, then heating is performed at a rate of 1°C / min to 530°C and held for 3 h, and finally, heating is continued at a rate of 1°C / min to 750°C and held for 3 h, after which the furnace is allowed to cool to room temperature. A one-dimensional tubular carbon wave-absorbing material is collected, denoted as Mtube.

[0042] Example 2:

[0043] The preparation method of the three-dimensional network carbon wave-absorbing material of this example is performed in the following steps:

[0044] (1) Take 1.50 g of melamine and add it to 100 mL of an ethanol aqueous solution (deionized water: ethanol, v:v = 1:1) and stir at 80°C until completely dissolved to obtain a melamine solution. Take 1.52 g of cyanuric acid and add it to 100 mL of an ethanol aqueous solution (deionized water: ethanol, v:v = 1:1) and stir at 80°C until completely dissolved to obtain a cyanuric acid solution. The obtained melamine solution is added dropwise to the obtained cyanuric acid solution and stirred at 80°C for 2 h. The product is transferred to a vacuum filtration bottle and washed with 80°C hot water, and then freeze-dried for 48 h to obtain a hydrogen-bonded organic framework material.

[0045] (2) Take 0.5 g of the hydrogen-bonded organic framework product and add it to 50 mL of a phenol-formaldehyde resin (molecular weight 1000) anhydrous ethanol solution with a concentration of 0.008 g / mL. After stirring for 12 h, centrifugation is performed to obtain a solid product, which is dried at 60°C, then placed in a sealed porcelain boat, and calcined in a tube furnace under an argon atmosphere. First, heating is performed at a rate of 2°C / min to 400°C and held for 2 h, then heating is performed at a rate of 1°C / min to 530°C and held for 3 h, and finally, heating is continued at a rate of 1°C / min to 750°C and held for 3 h, after which the furnace is allowed to cool to room temperature. A three-dimensional network carbon wave-absorbing material is collected, denoted as Mfoam.

[0046] Test Example:

[0047] Take 150 mg of one-dimensional tubular Mtube prepared in Example 1 and three-dimensional network Mfoam prepared in Example 2, respectively, and stir them with 3 g of PDMS, 0.3 g of acetone and 0.3 g of curing agent to be uniform, and then place them in a vacuum oven with a vacuum degree of 0.1 MPa for 30 min. Take out the mixture and add it to a mold, and then place it in a vacuum oven again and cure it at 100°C for 1 h to obtain a coaxial ring-shaped test sample with an inner diameter of 3.04 mm and an outer diameter of 7.00 mm. Place the prepared coaxial ring in the coaxial transmission line clamp of a vector network analyzer, connect the incident end and the receiving end, and test it in the frequency range of 2-18 GHz.

[0048] Figure 1 a and c are SEM images and HADDF-STEM images of the one-dimensional tubular Mtube prepared in Example 1, from which it can be seen that the length of the one-dimensional tubular Mtube is about 3-5 μm, the tube diameter is about 200-400 nm, and the wall thickness is less than 10 nm.

[0049] Figure 1 b and d are SEM images and HADDF-STEM images of the three-dimensional network Mfoam prepared in Example 2, from which it can be seen that the three-dimensional network Mfoam has a size of dozens of microns and has many micron-based and sub-micron holes; Figure 1 e and Figure 1 f are HRTEM images of the one-dimensional tubular Mtube prepared in Example 1 and the three-dimensional network Mfoam prepared in Example 2, respectively, and it can be seen that short-range ordered lattice fringes coexist with amorphous structures, in which the lattice fringes correspond to the (002) crystal plane of carbon, and both exhibit very similar microstructures.

[0050] Figure 2 a is an XRD spectrum of the one-dimensional tubular Mtube and the three-dimensional network Mfoam obtained in Example 1 and Example 2, and the results show that the samples exhibit typical amorphous characteristics, and the steamed bun-shaped diffraction peak near 2θ = 25° corresponds to the (002) crystal plane of carbon, and the wide and diffuse peak shape means that the carbon has a low degree of crystallinity; Figure 2 b is an FTIR spectrum of the one-dimensional tubular Mtube and the three-dimensional network Mfoam obtained in Example 1 and Example 2, and the infrared absorption peaks again indicate that the chemical structures of the two samples are very similar, and both contain a certain amount of triazine rings and abundant C-N groups.

[0051] Figure 3 are uv-Raman spectra of the one-dimensional tubular Mtube and the three-dimensional network Mfoam obtained in Example 1 and Example 2, and from the figures it can be seen that both groups of samples exhibit strong G scattering peaks at 1660 cm -1 , and no obvious D peaks or T peaks are observed, indicating that the carbon atoms in them are in sp2 Hybrid forms exist. Meanwhile, compared with the common sp 2 G peak position (1585 cm -1 ) of hybrid carbon materials, this phenomenon also indicates that the carbon adsorbent prepared by the present application may contain more olefinic carbon bonds. This is conducive to controlling the electrical conductivity of the adsorbent within a suitable range, thereby avoiding excessive skin effect.

[0052] Figure 4 a is the real part of the relative complex permittivity of the one-dimensional tubular Mtube and the three-dimensional network Mfoam obtained in Example 1 and Example 2. It can be seen that the real part of the permittivity of the three-dimensional network Mfoam is slightly larger than that of the one-dimensional tubular Mtube, both of which exhibit strong frequency dispersion phenomenon, but the spectral characteristics of the two curves are very similar, indicating that the change in morphology has no significant effect on the intrinsic electromagnetic response behavior. Figure 4 b is the imaginary part of the relative complex permittivity curve. Similarly, the imaginary part of the permittivity of the three-dimensional network Mfoam is also slightly larger than that of the one-dimensional tubular Mtube, while both of them maintain very similar spectral characteristics. The curve shows obvious multiple relaxation at high frequency, which may be due to the dipole and interface polarization relaxation induced by nitrogen doping, carbon nanocrystals and vacancy defects. The above results show that compared with the one-dimensional tubular Mtube, the three-dimensional network Mfoam exhibits stronger dielectric loss capability, which may be due to the three-dimensional network structure being more conducive to introducing carrier transport channels in the insulating matrix.

[0053] Figure 5 a is the comprehensive wave absorption performance of the one-dimensional tubular Mtube obtained in Example 1. It can be seen that in the thickness range of 1-5 mm, the effective absorption bandwidth of the absorbent can be adjusted to cover the frequency range of 5-18 GHz. Figure 5 b is the comprehensive wave absorption performance of the three-dimensional network Mfoam obtained in Example 2. It can be seen that in the thickness range of 1-5 mm, the effective absorption bandwidth of the absorbent can be adjusted to cover the frequency range of 4.5-18 GHz. This indicates the good impedance matching characteristics of the two absorbents in a wide frequency band.

[0054] Figure 6 is the wave absorption performance curve of the one-dimensional tubular Mtube and the three-dimensional network Mfoam obtained in Example 1 and Example 2, reflecting the maximum reflection loss and effective absorption bandwidth of each sample. It can be seen that the one-dimensional tubular Mtube has a minimum reflection loss (RL min ) of -55.32 dB at a matching thickness of 2.20 mm; the effective absorption bandwidth (EAB) ≤-10 dB of the one-dimensional tubular Mtube is 8.52 GHz at a thickness of 2.64 mm; while the three-dimensional network Mfoam has a RL minThe absorption rate is -26.49 dB; at a thickness of 2.42 mm, its EAB is 7.88 GHz. Both exhibit excellent microwave absorption performance.

[0055] Based on the above graphs and data analysis, this invention constructs morphology-controllable pure carbon microwave absorbing materials, namely one-dimensional tubular Mtubes and three-dimensional mesh Mfoams, through a self-assembly-self-sacrificial in-situ carbonization method. The larger porous structure improves the impedance matching characteristics of the materials. The carbon atoms in the materials have a low degree of order, with a large number of carbo-olefin bonds, and simultaneously contain abundant carbon nanocrystals, N-doped atoms, and vacancy defects. This structure can effectively control the conductivity of the materials within a suitable range while inducing strong polarization relaxation loss. Under the synergistic effect of impedance matching, resistive loss, and polarization relaxation loss, the fabricated one-dimensional tubular Mtubes and three-dimensional mesh Mfoams exhibit excellent microwave absorption performance, making them promising for future applications.

[0056] The above description is merely a preferred embodiment of the present invention. These specific embodiments are different implementations based on the overall concept of the present invention, and 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 scope of the technology 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. A method for preparing a high-performance carbon microwave absorbing material with controllable morphology, characterized in that, The method described: S1: Under heating conditions, melamine and cyanuric acid are dissolved in deionized water or in aqueous ethanol solution, respectively. Then, the melamine solution is added dropwise to the cyanuric acid solution, and the reaction is heated and stirred. After the reaction is completed, the mixture is washed with hot water by vacuum filtration and freeze-dried to obtain a hydrogen-bonded organic framework. S2: Add the hydrogen-bonded organic framework to the anhydrous ethanol solution of phenolic resin, stir to react, centrifuge, dry the solid product, and calcine under a protective atmosphere to obtain the carbon microwave absorbing material.

2. The method according to claim 1, characterized in that, In S1, the mass ratio of melamine to cyanuric acid is 1.5:(1-2), the ethanol concentration in the aqueous ethanol solution is 40-60 vol%, the melamine solution concentration is 0.01-0.02 g / mL, and the cyanuric acid solution concentration is 0.01-0.02 g / mL.

3. The method according to claim 1, characterized in that, The temperature for heating and stirring in S1 is 70-90℃, and the time is 1-3h.

4. The method according to claim 1, characterized in that, The mass ratio of hydrogen-bonded organic framework to phenolic resin in S2 is 0.5:(0.3-0.5), and the concentration of phenolic resin in the anhydrous ethanol solution is 6-10 mg / mL.

5. The method according to claim 1, characterized in that, Stir the reaction in S2 for 10-12 hours.

6. The method according to claim 1, characterized in that, The calcination procedure in S2 is as follows: at a rate of 1-3℃ / min, first heat to 350-450℃ and hold for 1-2.5h, then heat to 500-550℃ and hold for 2-4h, then continue to heat to 700-800℃ and hold for 1.5-4h, and finally cool to room temperature with the furnace after holding.

7. The one-dimensional tubular carbon microwave absorbing material prepared by the method according to any one of claims 1-6, characterized in that, When dissolved in deionized water, a one-dimensional tubular carbon microwave absorbing material is obtained, with a length of 3-5 μm, a diameter of 200-400 nm, and a wall thickness of <10 nm.

8. The three-dimensional mesh carbon microwave absorbing material prepared by the method according to any one of claims 1-6, characterized in that, When dissolved in an aqueous ethanol solution, a three-dimensional network of carbon microwave absorbing material is obtained, with a size of 10-40 μm and micron- and submicron-sized pores.

9. The application of the microwave absorbing material prepared by the method according to any one of claims 1-5, characterized in that, Within a thickness range of 1-5mm, it is used to absorb electromagnetic waves in the frequency range of 2-18GHz.

10. A microwave absorbing coating, said coating being prepared from a microwave absorbing material obtained by the method of any one of claims 1-5.

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