Laser thermo-chemical calcination electromagnetic wave absorber, preparation method and application thereof

Abstract

The application discloses a kind of laser thermochemical calcination electromagnetic wave absorber and its preparation method and application, belong to electromagnetic wave absorbing material technical field.The method of the present application includes the following steps: (1) iron source, cobalt source, nickel source are mixed with solvent, obtain iron cobalt nickel mixed solution;Phthalic acid is mixed with solvent, obtain phthalic acid solution;Iron cobalt nickel mixed solution and phthalic acid solution are mixed and reacted, after reaction, separate crude product, obtain multi-metal organic framework material precursor by purification, for standby;(2) in air atmosphere, using laser on the obtained multi-metal organic framework material precursor is carried out thermochemical calcination treatment, obtain electromagnetic wave absorber.The method uses laser thermochemical calcination process, simple and convenient process, lower cost, suitable for industrial large-scale production.The electromagnetic wave absorber prepared has excellent wave-absorbing performance, shows good shielding performance in terahertz wave band, and has good application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electromagnetic wave absorbing materials, and particularly relates to a laser thermal chemical calcination electromagnetic wave absorbing agent, a preparation method and application thereof. BACKGROUND

[0002] With the advent of the new era of the Internet of Things, wireless communication technology is expected to develop in the direction of multi-band and multi-field applications. For example, the currently defined sixth generation (6G) communication signal standard will use a higher frequency band of terahertz (THz), which will inevitably be combined with the current communication method at a low frequency of gigahertz (GHz).

[0003] Metal-organic framework (MOF) is a new type of multifunctional material formed by the coordination of metal ions and organic ligands. Due to the special properties of MOF, such as large specific surface area and high porosity, it has been widely used in catalysis, gas separation, adsorption and other fields. After carbonization, the organic ligand in MOF is carbonized into a porous carbon-based component, and the metal ion can be further reduced to metal oxide, metal nanoparticles or other components. By introducing various metal ions into MOF, nano-alloys can be further reduced. Therefore, the carbonized multi-metal-organic framework derivative effectively overcomes the shortcomings of the loss mechanism of single-component materials and optimizes the impedance of the absorber under matching conditions.

[0004] The carbonized MOF derivative has the advantages of low density, high mechanical strength and high stability, which is beneficial to reduce the density of the absorber. The carbon-based MOF derivative has high electronic conductivity, so it has strong resistance loss and high electromagnetic shielding performance in the terahertz wave band.

[0005] MOFs derived carbon-based composites as electromagnetic wave absorbers have been extensively studied. For example, Professor Ji Guangbin of Nanjing University of Aeronautics and Astronautics prepared Fe3O4@carbon composite absorbers using iron-based MOFs. The effective absorption bandwidth reached 4 GHz when the thickness was only 1.4 mm, and the lowest reflection loss reached -30.48 dB. Professor Che Renchao of Fudan University prepared a unique MOFs derived yolk-shell Ni@C@ZnO composite material. The lowest reflection loss reached -55.8 dB when the matching thickness was 2.5 mm, and the effective absorption bandwidth reached 4.1 GHz. In summary, the new wave-absorbing material using MOFs as a precursor has great research value, which exhibits excellent reflection loss and the advantage of light weight. However, the existing technology still has many shortcomings. The existing MOF derivative absorbers often have a single matching waveband, which cannot match the low-frequency waveband in the microwave band, further limiting the application of the absorber. Not only that, the application range of the existing absorber is narrow, and it cannot realize the shielding and absorption of electromagnetic waves in the high-frequency band such as the THz range. In addition, the carbonization process of the existing MOF derivative is high in cost, and it faces the problem of being unable to realize large-scale industrial production.

[0006] Therefore, it is necessary to develop a multi-band electromagnetic wave absorption and shielding material to address the above situation and solve the problems existing in the prior art. SUMMARY

[0007] In view of the above defects of the prior art, in the first aspect of the present application, a preparation method of an electromagnetic wave absorber which is simple and convenient in process and suitable for large-scale production is provided, comprising the following steps:

[0008] (1) mixing iron source, cobalt source and nickel source with solvent to obtain iron-cobalt-nickel mixed solution; mixing terephthalic acid with solvent to obtain terephthalic acid solution; mixing the iron-cobalt-nickel mixed solution and the terephthalic acid solution and reacting, separating the crude product after the reaction, and purifying to obtain a multi-metal organic framework material precursor for standby;

[0009] (2) in an air atmosphere, using laser to perform thermal chemical calcination treatment on the obtained multi-metal organic framework material precursor to obtain an electromagnetic wave absorber.

[0010] Preferably, in step (1), the types of iron source, cobalt source and nickel source include metal salts and their hydrates; wherein the iron salt includes one of iron acetate, iron nitrate and iron chloride; the cobalt salt includes one of cobalt acetate, cobalt nitrate and cobalt chloride; and the nickel salt includes one of nickel acetate, nickel nitrate and nickel chloride.

[0011] The metal salt type of the iron, cobalt and nickel sources is consistent, and the raw materials are more uniform and controllable.

[0012] The solvent used as a dispersion medium of the raw materials in the application is used to promote the dispersion of the raw materials and the smooth progress of the reaction, and the selection is diverse. Suitable types can be selected according to the type of the raw materials, and the amide solvent is a particularly suitable type. In order to achieve better process effect, preferably, in step (1), the solvent comprises one of N,N-dimethylformamide, dimethylacetamide, dimethylpropionamide, diethylformamide and diethylacetamide.

[0013] Preferably, in step (1), the concentration of the iron source, the cobalt source and the nickel source in the iron-cobalt-nickel mixed solution is independently 0.01-0.20 mmol / mL.

[0014] Preferably, in step (1), the concentration of the terephthalic acid solution is 0.2-1.0 mmol / mL.

[0015] Preferably, in step (1), the reaction temperature is 40-80℃, and the reaction time is 8-16h.

[0016] The power of the laser processing can be adjusted according to the type of the iron, cobalt and nickel sources. For example, when acetate is used, the power is 4.5W (or nitrate is used, the power is 6.0W; or chloride is used, the power is 7.5W). The material will achieve the optimal impedance matching in the low-frequency band, and the optimal wave absorption effect will be achieved. Higher energy will enhance the electrical conductivity and the dispersibility of the material, and affect the balance of the dielectric parameters and the magnetic permeability of the material. Preferably, in step (2), the laser power of the thermochemical calcination treatment is 4.5-9.0W, the laser pulse duration is 270fs-80ns, the working wavelength is 780-1064nm, and the working frequency is 10-50kHz.

[0017] In the preparation method of the application, terephthalic acid is used as a ligand of a multi-metal organic framework, and is reacted with an iron source, a cobalt source and a nickel source to obtain a multi-metal organic framework material precursor. Then, under the condition of laser treatment, the multi-metal organic framework material is carbonized at high temperature, and the ligand forms multi-layer graphene. The internal coordination metal ions are reduced by laser to form a multi-metal nano-alloy, which is coated in the graphene to avoid oxidation of the metal nanoparticles. By adjusting the laser parameters, the electrical conductivity of the material can be effectively adjusted by laser thermochemical calcination, thereby effectively optimizing the dielectric loss performance of the material. Similarly, the adjustment of the laser parameters can also control the particle size and dispersity of the magnetic nano-alloy, thereby effectively adjusting the magnetic loss capacity of the material.

[0018] In a second aspect of the present application, an electromagnetic wave absorber with excellent electromagnetic wave absorption capacity and wide applicability is provided, which is prepared by the method provided in the first aspect of the present application, and comprises porous graphene with a layered structure and magnetic nano-alloy in the form of particles formed by iron, cobalt and nickel, which is uniformly distributed and coated in the porous graphene.

[0019] The multilayer graphene can not only ensure high conductivity of the electromagnetic wave absorber, but also enhance the dielectric loss inside the electromagnetic wave absorber, thereby improving the electromagnetic wave absorption performance of the material. Preferably, in the electromagnetic wave absorber, the number of layers of the porous graphene is 3-7.

[0020] The small particle size and large dispersity of the magnetic nanoparticles can enable the material to realize matching of low-frequency waveband absorption. Preferably, in the electromagnetic wave absorber, the particle size of the magnetic nano-alloy is 3-100 nm.

[0021] The laser induces carbonization of MOF organic ligands into multilayer graphene and reduction of metal ions into magnetic nano-alloy by means of thermal chemical calcination. After laser treatment, a porous structure is formed on the surface of the material, which makes the material have a high specific surface area, improves the interface polarization capacity, increases the number of times of reflection and absorption of electromagnetic waves inside the material, and enables the electromagnetic wave absorber to have excellent electromagnetic wave absorption performance while reducing the density of the composite material. A complex interface is formed between the graphene and the magnetic nano-alloy, which enhances the interface polarization and improves the polarization loss capacity of the material; and by adjusting the laser parameters, impedance matching of the dielectric constant and magnetic permeability of the material can be realized, thereby achieving better electromagnetic absorption performance.

[0022] In a third aspect of the present application, the electromagnetic wave absorber of the second aspect of the present application is provided, and specifically, the electromagnetic wave absorber is applied as an electromagnetic wave absorbing material in absorption and shielding of electromagnetic waves.

[0023] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0024] The present application provides a preparation method of an electromagnetic wave absorber, which adopts a laser thermal chemical calcination process, has a simple and convenient process and low cost, and is suitable for industrial large-scale production.

[0025] The present application provides an electromagnetic wave absorber, which has excellent electromagnetic wave absorption performance, can realize matching of low-frequency microwave absorption, has high conductivity, and exhibits good shielding performance in the terahertz (THz) waveband.

[0026] The present application also provides an application of the electromagnetic wave absorber, which has good applicability as an electromagnetic wave absorbing material in absorption and shielding of electromagnetic waves. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 Scanning electron microscope (SEM) image of the electromagnetic wave absorber prepared in Example 1;

[0028] Figure 2 In the figure, (a) is a transmission electron microscope (TEM) image of the electromagnetic wave absorber prepared in Example 1; (b) is a size distribution of the nano-alloy in the electromagnetic wave absorber; (c) is a selected area electron diffraction (SAED) pattern of the electromagnetic wave absorber;

[0029] Figure 3 X-ray diffraction (XRD) pattern of the electromagnetic wave absorber prepared in Example 1;

[0030] Figure 4 In the figure, (a) is a reflection loss spectrum of the electromagnetic wave absorber prepared in Example 1; (b) is a corresponding impedance matching diagram projection thereof;

[0031] Figure 5 Test results of electromagnetic shielding performance of the electromagnetic wave absorber prepared in Example 1 in the terahertz (THz) wave band. DETAILED DESCRIPTION

[0032] The present application will be further described in the following examples, but the present application is not limited in the scope of the examples. The experimental methods not specified in the following examples are selected according to the conventional methods and conditions, or according to the instructions of the commercial products.

[0033] In the following examples, the laser system uses a nanosecond laser (YLP-0.5-80-10, IPG photonics) as the laser source.

[0034] Example 1

[0035] A preparation method of an electromagnetic wave absorber, the steps of which are as follows:

[0036] (1) 0.1 mmol of iron acetate hexahydrate, 0.3 mmol of cobalt acetate hexahydrate, and 0.6 mmol of nickel acetate hexahydrate are fully stirred and mixed with 10 mL of N,N-dimethylformamide to obtain a mixed solution of iron, cobalt and nickel; 1.0 mmol of terephthalic acid is fully stirred and mixed with 5 mL of N,N-dimethylformamide to obtain a terephthalic acid solution; the mixed solution of iron, cobalt and nickel and the terephthalic acid solution are mixed and stirred uniformly, and then reacted at 50°C for 12 h; after the reaction is completed, the precipitate is collected by centrifugation to obtain a crude product, which is washed and dried to obtain a multi-metal organic framework material precursor, which is ready for use;

[0037] (2) In an air atmosphere, the obtained multi-metal organic framework material precursor is subjected to a thermal chemical calcination treatment by using a nanosecond laser, the laser power is set to 4.5 W, the laser pulse duration is 80 ns, the working wavelength is 1064 nm, and the working frequency is 20 kHz. Under the above conditions, the multi-metal organic framework material precursor is converted into a graphene-coated magnetic nano-alloy material (denoted as LIMA), and an electromagnetic wave absorber is obtained.

[0038] The micro-morphology of the electromagnetic wave absorber prepared by using the multi-metal organic framework as a precursor in the embodiment is observed by using a scanning electron microscope (SEM). As shown in FIG. 2, Figure 1 the prepared electromagnetic wave absorber presents a porous structure, and the magnetic nano-alloy (i.e., the light-colored particles in the figure) is dispersed in the form of particles in the porous carbon matrix. According to the high-magnification electron microscope image, the particle size of the nanoparticles is statistically analyzed, and the main particle size is in the range of 3-200 nm.

[0039] The micro-morphology of the electromagnetic wave absorber in the embodiment is observed by using a transmission electron microscope (TEM). As shown in FIG. 3, Figure 2 (a), the TEM image of the electromagnetic wave absorber reveals the high uniformity of the distribution and wrapping of the magnetic nano-alloy nanoparticles on the graphene substrate. Meanwhile, the graphene lattice can also be further observed in the TEM image, and the graphene lattice spacing is measured to be 0.34 nm, further verifying the stable preparation of graphene in the method. As shown in FIG. 3, Figure 2 (b), the size distribution of the magnetic nano-alloy is statistically analyzed, and the magnetic nano-alloy particles are normally distributed in the range of 3-19 nm, verifying the potential of the method for the nanoscale preparation of nano-alloys. Figure 2 (c), the electron diffraction (SAED) image shows a series of obvious electron diffraction rings, which clearly proves that the graphene-wrapped Fe / Co / Ni ternary alloy is composed of multiple crystal nanoparticles. This crystallinity emphasizes the robustness and stability of the synthesized nanomaterials.

[0040] The electromagnetic wave absorber in the embodiment is characterized by X-ray diffraction (XRD). As shown in FIG. 4, Figure 3 the smallest peak at 26.36° corresponds to the (002) lattice plane of graphene. The three peaks at 44.193°, 51.441° and 75.759° correspond to the (111), (200) and (220) planes of the face-centered cubic structure Fe / Co / Ni, respectively.

[0041] The electromagnetic performance of the material is measured by using a conventional coaxial transmission reflection method, the material is mixed with paraffin in a certain proportion and embedded into a coaxial line, so as to obtain a reflection loss spectrum reflecting the wave absorption performance of the sample. As shown in FIG. 5, Figure 4(a) shows that LIMA exhibits excellent electromagnetic wave absorption performance, when the sample mixing ratio is 25wt.%, the coaxial ring thickness is 5.1mm, the minimum reflection loss reaches-50.94dB. Corresponding Figure 4 (b) shows the impedance matching diagram projection, which ensures the impedance matching performance in a wide frequency domain.

[0042] The electromagnetic shielding performance of the electromagnetic wave absorber in the terahertz (THz) wave band was tested. The evaluation of terahertz shielding is based on the combined application of transmission and reflection modes in a conventional terahertz time-domain spectroscopy (THz-tds) system. As shown in Figure 5 LIMA exhibits good electromagnetic wave shielding performance, and the thin film exhibits good electromagnetic shielding performance under three different thicknesses. And under the thickness of 0.886mm, the reflection loss value can even reach 99.8dB. Under this condition, it also shows good terahertz shielding effect.

[0043] Example 2

[0044] A preparation method of an electromagnetic wave absorber, the steps of which are as follows:

[0045] (1) 0.1mmol of ferric nitrate, 0.3mmol of cobalt nitrate, 0.6mmol of nickel nitrate and 10mL of N,N-dimethylformamide were fully stirred and mixed to obtain a ferric-cobalt-nickel mixed solution; 1.0mmol of terephthalic acid and 5mL of N,N-dimethylformamide were fully stirred and mixed to obtain a terephthalic acid solution; the ferric-cobalt-nickel mixed solution and the terephthalic acid solution were mixed and stirred uniformly and reacted at 50℃ for 12h, after the reaction was completed, the precipitate was collected by centrifugation to obtain a crude product, which was washed and dried to obtain a multi-metal organic framework material precursor, which was reserved;

[0046] (2) In an air atmosphere, the obtained multi-metal organic framework material precursor was subjected to a thermal chemical calcination treatment by using a nanosecond laser, the laser power was set to 6.0W, the laser pulse duration was 80ns, the working wavelength was 1064nm, and the working frequency was 20kHz. Under this condition, the multi-metal organic framework material precursor was converted into a graphene-coated magnetic nano-alloy material, i.e. the electromagnetic wave absorber.

[0047] Example 3

[0048] A preparation method of an electromagnetic wave absorber, the steps of which are as follows:

[0049] (1) 0.1 mmol of iron chloride, 0.3 mmol of cobalt chloride, and 0.6 mmol of nickel chloride were mixed with 10 mL of N,N-dimethylformamide to obtain a mixed solution of iron, cobalt, and nickel; 1.0 mmol of terephthalic acid was mixed with 5 mL of N,N-dimethylformamide to obtain a terephthalic acid solution; the mixed solution of iron, cobalt, and nickel and the terephthalic acid solution were mixed and stirred uniformly, and reacted at 50°C for 12 h; after the reaction was completed, the precipitate was collected by centrifugation to obtain a crude product, which was washed and dried to obtain a multi-metal organic framework material precursor, which was reserved for use;

[0050] (2) The multi-metal organic framework material precursor obtained was subjected to thermal chemical calcination treatment in an air atmosphere by using a nanosecond laser, the laser power was set to 7.5 W, the laser pulse duration was 80 ns, the working wavelength was 1064 nm, and the working frequency was 20 kHz; under the above conditions, the multi-metal organic framework material precursor was converted into a graphene-coated magnetic nano-alloy material, thereby obtaining an electromagnetic wave absorber.

[0051] Example 4

[0052] A preparation method of an electromagnetic wave absorber, comprising the following steps:

[0053] (1) 0.1 mmol of iron chloride, 0.3 mmol of cobalt chloride, and 0.6 mmol of nickel chloride were mixed with 10 mL of N,N-dimethylformamide to obtain a mixed solution of iron, cobalt, and nickel; 1.0 mmol of terephthalic acid was mixed with 5 mL of N,N-dimethylformamide to obtain a terephthalic acid solution; the mixed solution of iron, cobalt, and nickel and the terephthalic acid solution were mixed and stirred uniformly, and reacted at 50°C for 12 h; after the reaction was completed, the precipitate was collected by centrifugation to obtain a crude product, which was washed and dried to obtain a multi-metal organic framework material precursor, which was reserved for use;

[0054] (2) The multi-metal organic framework material precursor obtained was subjected to thermal chemical calcination treatment in an air atmosphere by using a femtosecond laser, the laser power was set to 9 W, the laser pulse duration was 270 fs, the working wavelength was 1036 nm, and the working frequency was 36 kHz; under the above conditions, the multi-metal organic framework material precursor was converted into a graphene-coated magnetic nano-alloy material, thereby obtaining an electromagnetic wave absorber.

[0055] Example 5

[0056] (1) 0.1 mmol of iron chloride, 0.3 mmol of cobalt chloride, and 0.6 mmol of nickel chloride were mixed with 10 mL of N,N-dimethylformamide to obtain a mixed solution of iron, cobalt, and nickel; 1.0 mmol of terephthalic acid was mixed with 5 mL of N,N-dimethylformamide to obtain a terephthalic acid solution; the mixed solution of iron, cobalt, and nickel and the terephthalic acid solution were mixed and stirred uniformly, and reacted at 40°C for 16 h; after the reaction was completed, the precipitate was collected by centrifugation to obtain a crude product, which was washed and dried to obtain a multi-metal organic framework material precursor, which was reserved for use;

[0057] (2) The multi-metal organic framework material precursor obtained was subjected to thermal chemical calcination treatment in an air atmosphere by using a nanosecond laser, the laser power was set to 4.5 W, the laser pulse duration was 80 ns, the working wavelength was 780 nm, and the working frequency was 50 kHz; under the above conditions, the multi-metal organic framework material precursor was converted into a graphene-coated magnetic nano-alloy material, thereby obtaining an electromagnetic wave absorber.

[0058] Example 6

[0059] (1) 0.1 mmol of iron chloride, 0.3 mmol of cobalt chloride, and 0.6 mmol of nickel chloride were mixed with 10 mL of N,N-dimethylformamide to obtain a mixed solution of iron, cobalt, and nickel; 1.0 mmol of terephthalic acid was mixed with 5 mL of N,N-dimethylformamide to obtain a terephthalic acid solution; the mixed solution of iron, cobalt, and nickel and the terephthalic acid solution were mixed and stirred uniformly, and reacted at 80°C for 8 h; after the reaction was completed, the precipitate was collected by centrifugation to obtain a crude product, which was washed and dried to obtain a multi-metal organic framework material precursor, which was reserved for use;

[0060] (2) The multi-metal organic framework material precursor obtained was subjected to thermal chemical calcination treatment in an air atmosphere by using a nanosecond laser, the laser power was set to 4.5 W, the laser pulse duration was 80 ns, the working wavelength was 1064 nm, and the working frequency was 10 kHz; under the above conditions, the multi-metal organic framework material precursor was converted into a graphene-coated magnetic nano-alloy material, thereby obtaining an electromagnetic wave absorber.

[0061] The above describes preferred embodiments of the present application in detail. It should be understood that those skilled in the art can make many modifications and changes without creative labor based on the concept of the present application. Therefore, any technical solutions obtained by logical analysis, reasoning, or limited experiments based on the prior art according to the concept of the present application shall be within the protection scope defined by the claims.

Claims

1. An electromagnetic absorbing agent, characterized in that, The electromagnetic absorbing agent includes porous graphene with a layered structure and a granular magnetic nano-alloy formed of iron, cobalt and nickel, with the magnetic nano-alloy being uniformly distributed and coated within the porous graphene. The preparation method of the electromagnetic absorbing agent includes the following steps: (1) Mix the iron source, cobalt source, and nickel source with the solvent to obtain an iron-cobalt-nickel mixture; mix terephthalic acid with the solvent to obtain a terephthalic acid solution; mix the iron-cobalt-nickel mixture and the terephthalic acid solution and react them. After the reaction is completed, separate the crude product and purify it to obtain a precursor of a multi-metal-organic framework material for later use. (2) In an air atmosphere, the obtained multi-element metal-organic framework material precursor is subjected to thermochemical calcination treatment by laser to obtain an electromagnetic absorbing agent; The laser power of the thermochemical calcination treatment is 4.5~9.0W, the laser pulse duration is 270fs~80ns, the working wavelength is 780~1064nm, and the working frequency is 10~50kHz.

2. The electromagnetic absorbing agent according to claim 1, characterized in that: In step (1), the types of iron source, cobalt source and nickel source include metal salts and their hydrates; wherein, iron salt includes one of ferric acetate, ferric nitrate and ferric chloride; cobalt salt includes one of cobalt acetate, cobalt nitrate and cobalt chloride; and nickel salt includes one of nickel acetate, nickel nitrate and nickel chloride.

3. The electromagnetic absorbing agent according to claim 2, characterized in that: The anion types of the iron salt, cobalt salt, and nickel salt are kept consistent.

4. The electromagnetic absorbing agent according to claim 1, characterized in that: The concentrations of the iron, cobalt, and nickel sources in the iron-cobalt-nickel mixture are each 0.01~0.20 mmol / mL; the concentration of the terephthalic acid solution is 0.2~1.0 mmol / mL.

5. The electromagnetic absorbing agent according to claim 1, characterized in that: In step (1), the reaction temperature is 40~80℃ and the reaction time is 8~16h.

6. The electromagnetic absorbing agent according to claim 1, characterized in that: The porous graphene has a layer distribution of 3 to 7 layers.

7. The electromagnetic absorbing agent according to claim 1, characterized in that: The magnetic nanoalloy has a particle size distribution of 3~100 nm.

8. The application of an electromagnetic absorbing agent as described in any one of claims 1 to 7, characterized in that: The application of electromagnetic absorbing agents as electromagnetic absorbing materials in absorbing and shielding electromagnetic waves.

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