Preparation method of cobalt-based metal organic framework derivative absorber with nanocomposite structure

Abstract

The present invention belongs to the field of materials, and specifically relates to a method for preparing a cobalt-based metal organic framework derivative absorber with a nano-composite structure, which solves the technical problem that cobalt-based metal organic framework derivatives are difficult to achieve a high absorption bandwidth. First, a metal organic framework precursor is prepared by a solvent thermal method, and cobalt nitrate hexahydrate, terephthalic acid and polyvinylpyrrolidone K30 are dissolved in a mixed solution of deionized water, anhydrous ethanol and N,N-dimethylformamide, and stirred to obtain a uniform and stable solution. Subsequently, the solution is sealed in a polytetrafluoroethylene-lined stainless steel reactor and subjected to a solvent thermal reaction. After cooling, the precipitate is collected by centrifugation, washed several times with deionized water and then dried. Finally, the product is carbonized at high temperature in a tube furnace under a protective atmosphere, and the sintered product is collected to obtain a cobalt-based metal organic framework derivative absorber with a nano-composite structure.

Description

Technical Field

[0001] The invention belongs to the field of materials, and in particular relates to a method for preparing a cobalt-based metal organic framework derivative wave absorbing agent with a nano-composite structure. Background Art

[0002] With the rapid development of information and communication technology, various electronic devices, especially fifth-generation (5G) mobile communication devices, have greatly improved information exchange by providing extremely high data transmission rates and extremely low latency. As a medium for transmitting signals, the reception and generation of electromagnetic waves have covered various scenarios in social environments and sensitive electronic devices in industrial environments. High-frequency electromagnetic waves have a high energy density and pose a serious threat to the stable operation of sensitive devices and human health. Therefore, this difficulty has become a problem that must be overcome, and the exploration of electromagnetic wave absorbing materials is imminent.

[0003] Carbon-based nanomaterials (carbon nanotubes and graphene) have been widely studied as candidate materials for electromagnetic wave absorbers due to their relatively low density and controllable dielectric parameters. However, due to their non-magnetic properties, their magnetic permeability is much lower than their dielectric constant, resulting in imperfect impedance matching and reduced absorption capacity. Recently, MXene has been considered as a promising electromagnetic wave absorber, but the conductivity of pure MXene is too high to be an excellent electromagnetic wave absorber. Although the above materials exhibit electromagnetic wave absorption performance based on soft magnetic or dielectric properties, the construction of new nanocomposites by combining magnetic and dielectric components is expected to achieve the coupling of magnetic and dielectric absorption. Therefore, there is an urgent need to develop new and efficient electromagnetic wave absorbers to meet this demand. At the same time, it is also expected that the manufacture of such nanocomposites with more porous structures will help to further regulate electromagnetic wave absorption. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing a cobalt-based metal-organic framework derivative absorber with a nanocomposite structure, namely, using a solvent thermal and high-temperature carbonization method to prepare a multilayer composite structure loaded with nanoparticles, thereby solving the technical problem that cobalt-based metal-organic framework derivatives are difficult to achieve a high absorption bandwidth.

[0005] The technical solution of the present invention is:

[0006] A method for preparing a cobalt-based metal-organic framework derivative absorber with a nanocomposite structure comprises the following steps: first, a metal-organic framework precursor is prepared by a solvothermal method, wherein cobalt nitrate hexahydrate, terephthalic acid, and polyvinylpyrrolidone K30 are dissolved in a mixed solution of deionized water, anhydrous ethanol, and N,N-dimethylformamide, and stirred to obtain a uniform and stable solution; then, the obtained solution is sealed in a polytetrafluoroethylene-lined stainless steel reactor and subjected to a solvothermal reaction. After cooling, a precipitate is collected by centrifugation, washed with deionized water, and then dried; finally, the product is carbonized at high temperature in a tube furnace under a protective atmosphere, and the sintered product is collected, which is the cobalt-based metal-organic framework derivative absorber with a nanocomposite structure.

[0007] The preparation method of the cobalt-based metal-organic framework derivative absorber with a nanocomposite structure comprises the following steps: the purity of cobalt nitrate hexahydrate is ≥98.5wt%, the purity of terephthalic acid is ≥99wt%, polyvinylpyrrolidone K30 is of premium purity, deionized water is of analytical purity, the purity of anhydrous ethanol is ≥99.7wt%, and the purity of N,N-dimethylformamide is ≥99.5wt%.

[0008] The preparation method of the cobalt-based metal-organic framework derivative absorber with a nanocomposite structure comprises 1.748 g of cobalt nitrate hexahydrate, 0.6 g of terephthalic acid, 4.0 g of polyvinylpyrrolidone K30, and 40 mL of deionized water, anhydrous ethanol, and N,N-dimethylformamide.

[0009] The preparation method of the cobalt-based metal organic framework derivative absorber with a nanocomposite structure has a stirring time of 20 to 40 minutes and a solvent thermal reaction condition of keeping the temperature at 180 to 220° C. for 10 to 15 hours.

[0010] The preparation method of the cobalt-based metal organic framework derivative absorber with a nano-composite structure comprises the following drying conditions: vacuum drying at 50-70° C. for 6-10 hours.

[0011] The method for preparing the cobalt-based metal-organic framework derivative absorber with a nanocomposite structure comprises the following process parameters for high-temperature carbonization in a tube furnace: a heating rate of 8 to 12°C / min, a holding temperature of 700°C ± 10°C, and a holding time of 4 to 6 hours; and a protective atmosphere of a mixed gas of 95% Ar and 5% H2 by volume.

[0012] The method for preparing the cobalt-based metal organic framework derivative wave absorber with a nano-composite structure has the structural characteristics of the cobalt-based metal organic framework derivative as follows: a composite structure of two or more layers of loaded nanoparticles.

[0013] The preparation method of the cobalt-based metal organic framework derivative absorber with a nano-composite structure is as follows: the basic skeleton of the cobalt-based metal organic framework derivative is a typical fan-shaped morphology, and its overall size is 50 to 100 μm. The surface of each single layer is covered with nanoparticles, and the material of the nanoparticles is elemental cobalt.

[0014] The application of the cobalt-based metal organic framework derivative wave absorbing agent with a nano-composite structure is that the cobalt-based metal organic framework derivative is used as a wave absorbing material in the frequency band between 11 and 18 GHz.

[0015] The application of the cobalt-based metal organic framework derivative absorber with a nanocomposite structure is to mix the cobalt-based metal organic framework derivative with a medium that absorbs electromagnetic waves as the absorbing material; in terms of mass percentage, the cobalt-based metal organic framework derivative comprises 30 wt.% to 60 wt.% of the medium, and the rest is the medium that absorbs electromagnetic waves.

[0016] The design idea of the present invention is:

[0017] Currently, pure cobalt-based metal-organic framework derivatives have a low effective bandwidth, generally below 6 GHz, which limits their widespread application. The present invention aims to prepare pure cobalt-based metal-organic framework derivatives with novel nanocomposite structures. These nanocomposite structures enhance the reflection of electromagnetic waves within the material, resulting in materials with superior absorption properties compared to other similar materials. First, a metal-organic framework precursor is prepared using a solvothermal method. Cobalt nitrate hexahydrate, terephthalic acid, and polyvinylpyrrolidone K30 are dissolved in a mixed solution of deionized water, anhydrous ethanol, and N,N-dimethylformamide, and stirred to obtain a uniform and stable solution. The resulting solution is then sealed in a polytetrafluoroethylene-lined stainless steel reactor for a solvothermal reaction. After cooling, the precipitate is collected by centrifugation, washed with deionized water, and dried. Finally, the product is carbonized at high temperature in a tube furnace under a protective atmosphere. The sintered product is collected to obtain a cobalt-based metal-organic framework derivative absorber with a nanocomposite structure.

[0018] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0019] 1. The present invention adopts a simple solvent thermal method to prepare a metal organic framework precursor, and synthesizes a new cobalt-based metal organic framework derivative through solvent thermal and sintering processes. The composite material has a layered porous layered structure and is loaded with nanoparticles on the layers, which can be used in the field of electromagnetic wave absorption.

[0020] 2. The preparation process of the present invention is simple, easy to operate, low in cost, safe, reliable and highly reproducible.

[0021] 3. The present invention improves the current situation that the effective bandwidth of pure cobalt-based metal-organic framework derivatives is lower than 6 GHz, and broadens the application prospects of pure cobalt-based metal-organic framework derivatives. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 X-ray diffraction spectrum of the cobalt-based metal organic framework derivative absorber with nanocomposite structure in the embodiment; in the figure, the abscissa 2θ (degree) is the diffraction angle, and the ordinate Intensity (au) is the relative intensity.

[0023] Figure 2 Scanning electron microscope image (morphology image) of the cobalt-based metal organic framework derivative absorber with a nanocomposite structure in the embodiment.

[0024] Figure 3 The magnetization curve of the cobalt-based metal organic framework derivative absorber with a nanocomposite structure in the embodiment at 300K (room temperature); in the figure, the abscissa H (kOe) is the magnetic field intensity, and the ordinate M (emu / g) is the magnetization intensity.

[0025] Figure 4 Frequency dependence of electromagnetic parameters of a cobalt-based metal-organic framework-derived absorber with a nanocomposite structure in an embodiment. (a) Frequency dependence of the real part of the dielectric constant ε', (b) Frequency dependence of the imaginary part of the dielectric constant ε", (c) Frequency dependence of the real part of the magnetic permeability μ', and (d) Frequency dependence of the imaginary part of the magnetic permeability μ". The horizontal axis (Frequency (GHz)) represents frequency.

[0026] Figure 5 The relationship between the reflection loss of the nanocomposite structured cobalt-based metal-organic framework derivative absorber and frequency in the embodiments is shown. Specifically, (a) the relationship between the reflection loss of the nanocomposite structured cobalt-based metal-organic framework derivative absorber and frequency is shown, (b) the relationship between the reflection loss of the nanocomposite structured cobalt-based metal-organic framework derivative absorber and frequency is shown, (c) the relationship between the reflection loss of the nanocomposite structured cobalt-based metal-organic framework derivative absorber and frequency is shown, and (d) the relationship between the reflection loss of the nanocomposite structured cobalt-based metal-organic framework derivative absorber and frequency is shown. In the figures, the horizontal axis is frequency (GHz), and the vertical axis is reflection loss (RL (dB). DETAILED DESCRIPTION

[0027] In a specific implementation, the preparation method of the nanocomposite cobalt-based metal-organic framework derivative absorber of the present invention is as follows: First, a metal-organic framework precursor is prepared using a solvothermal method. Cobalt nitrate hexahydrate, terephthalic acid, and polyvinylpyrrolidone K30 are dissolved in a mixed solution of deionized water, anhydrous ethanol, and N,N-dimethylformamide, and stirred to obtain a uniform and stable solution. Subsequently, the resulting solution is sealed in a polytetrafluoroethylene-lined stainless steel reactor for a solvothermal reaction. After cooling, the precipitate is collected by centrifugation, washed 2-6 times with deionized water, and then dried. Finally, the product is carbonized at high temperature in a tube furnace under a protective atmosphere, and the sintered product is collected.

[0028] The present invention is further described in detail below through examples and drawings.

[0029] Example

[0030] In this embodiment, the preparation method of the nanocomposite structured cobalt-based metal organic framework derivative absorber is as follows:

[0031] First, 1.748 g of cobalt nitrate hexahydrate, 0.6 g of terephthalic acid, and 4.0 g of polyvinylpyrrolidone K30 were dissolved in a mixed solution containing 40 ml of deionized water, 40 ml of anhydrous ethanol, and 40 ml of N,N-dimethylformamide and stirred for 30 minutes to obtain a uniform and stable solution. Next, the resulting solution was sealed in a polytetrafluoroethylene-lined stainless steel reactor and kept at 200°C for 12 hours. The resulting pink precipitate was then washed three times with deionized water and vacuum-dried at 60°C for 8 hours. Finally, the resulting product was heated in a tube furnace at a rate of 10°C / min under a protective atmosphere of Ar (95%) / H2 (5%) by volume, with a holding temperature of 700°C for 5 hours. The sintered product was collected to obtain a multilayer composite structure of a cobalt-based metal-organic framework derivative loaded with nanoparticles.

[0032] like Figure 1 As shown, the main phase of the obtained multilayer composite structure of cobalt-based metal-organic framework derivatives loaded with nanoparticles is elemental cobalt.

[0033] like Figure 2 The resulting nanoparticle-loaded cobalt-based metal-organic framework derivative multilayer composite structure is shown. Its structural characteristics are: a multilayer composite structure loaded with nanoparticles. The basic framework has a typical fan-shaped morphology, with an overall size of approximately 80 μm. Each monolayer is covered with nanoscale spherical particles made of elemental cobalt.

[0034] like Figure 3 As shown, the saturation magnetization intensity of the cobalt-based metal-organic framework derivative absorber with a nanocomposite structure is 134.93emu / g, showing strong magnetism.

[0035] like Figure 4 As shown, 30 wt.%, 40 wt.%, 50 wt.%, and 60 wt.% of a cobalt-based metal-organic framework derivative absorber sample having a nanocomposite structure were mixed with 70 wt.%, 60 wt.%, 50 wt.%, and 40 wt.% of paraffin (a medium for absorbing electromagnetic waves), respectively, by mass percentage. The electromagnetic properties measured at room temperature showed that the real part of the dielectric constant ε' was between 5 and 35 in the range of 2 to 18 GHz, the imaginary part of the dielectric constant ε" was between 5 and 55 in the range of 2 to 18 GHz, the real part of the complex magnetic permeability μ' was between 0.7 and 1.35 in the range of 2 to 18 GHz, and the imaginary part of the complex magnetic permeability μ" was between 0 and 0.25 in the range of 2 to 18 GHz.

[0036] like Figure 5 As shown, the relationship between the reflection loss and frequency of the cobalt-based metal-organic framework derivative absorber samples with a nanocomposite structure of 30wt.%, 40wt.%, 50wt.%, and 60wt.% is given in terms of mass percentage. The curve shows that as the measured sample content increases from 30wt.% to 60wt.%, when the sample ratio reaches 30wt.%, it has good absorbing performance in the high frequency range (11-18GHz), and the reflection loss approaches -32.92dB (>99.99% absorption), and has an effective bandwidth of 6.9GHz when d=2.5mm. In summary, it has strong absorbing performance in the high frequency region of 11-18GHz.

[0037] Comparative Example 1

[0038] In this comparative example, 1.748 g of cobalt nitrate hexahydrate, 0.6 g of terephthalic acid and 4.0 g of polyvinylpyrrolidone K30 were dissolved in a mixed solution containing 40 ml of deionized water, 40 ml of anhydrous ethanol and 40 ml of N,N-dimethylformamide, and stirred for 30 minutes to obtain a uniform and stable solution. Next, the mixed solution was sealed in a polytetrafluoroethylene-lined stainless steel reactor and kept warm at 200°C for 12 hours. Then, the obtained pink precipitate was washed three times with deionized water and vacuum dried at 60°C for 8 hours. Finally, the obtained product was heated at a rate of 10°C / min in a tube furnace under a protective atmosphere of Ar (95%) / H2 (5%) by volume, and the holding temperature was 600°C for 5 hours to obtain a multilayer composite structure of a cobalt-based metal-organic framework derivative loaded with nanoparticles. However, due to insufficient heating temperature in the tube furnace, the electromagnetic matching is poor, resulting in poor wave absorption performance. Its performance indicators are as follows: the optimal reflection loss is -6.9dB at 13.7GHz, and there is no effective bandwidth.

[0039] Comparative Example 2

[0040] In this comparative example, 1.748 g of cobalt nitrate hexahydrate, 0.6 g of terephthalic acid and 4.0 g of polyvinylpyrrolidone K30 were dissolved in a mixed solution containing 40 ml of deionized water, 40 ml of anhydrous ethanol and 40 ml of N,N-dimethylformamide, and stirred for 30 minutes to obtain a uniform and stable solution. Next, the mixed solution was sealed in a polytetrafluoroethylene-lined stainless steel reactor and kept warm at 200°C for 12 hours. Then, the obtained pink precipitate was washed three times with deionized water and vacuum dried at 60°C for 8 hours. Finally, the obtained product was heated at a rate of 10°C / min in a tube furnace under a protective atmosphere of Ar (95%) / H2 (5%) by volume, and the holding temperature was 800°C for 5 hours to obtain a multilayer composite structure of a cobalt-based metal-organic framework derivative loaded with nanoparticles. However, due to the high temperature heated in the tube furnace, the electromagnetic matching is poor, so the absorption performance is poor. Its performance indicators are as follows: the optimal reflection loss is -14.99dB at 14.6GHz, and the maximum effective bandwidth is 5.9GHz.

[0041] The above-described embodiments merely represent implementation methods of the present invention and are not to be construed as limiting the scope of the present invention, nor are they to impose any formal limitations on the structure of the present invention. It should be noted that a person skilled in the art may make various changes and improvements without departing from the scope of the present invention, and all such changes and improvements fall within the scope of protection of the present invention.

Claims

1. A method for preparing a cobalt-based metal organic framework derivative absorber having a nanocomposite structure, characterized in that: First, a metal-organic framework precursor was prepared using a solvothermal method. Cobalt nitrate hexahydrate, terephthalic acid, and polyvinylpyrrolidone K30 were dissolved in a mixture of deionized water, anhydrous ethanol, and N,N-dimethylformamide and stirred to obtain a uniform and stable solution. The resulting solution was then sealed in a polytetrafluoroethylene-lined stainless steel reactor for a solvothermal reaction. After cooling, the precipitate was collected by centrifugation, washed with deionized water, and dried. Finally, the product was carbonized at high temperature in a tube furnace under a protective atmosphere. The sintered product was collected to obtain a cobalt-based metal-organic framework derivative absorber with a nanocomposite structure. The structural characteristics of cobalt-based metal-organic framework derivatives are: a composite structure with more than two layers of loaded nanoparticles; The basic skeleton of the cobalt-based metal-organic framework derivative is a typical fan-shaped morphology with an overall size of 50 to 100 μm. The surface of each monolayer is covered with nanoparticles, and the material of the nanoparticles is elemental cobalt.

2. The method for preparing the cobalt-based metal organic framework derivative absorber having a nanocomposite structure according to claim 1, characterized in that: The purity of cobalt nitrate hexahydrate is ≥98.5 wt%, the purity of terephthalic acid is ≥99 wt%, polyvinylpyrrolidone K30 is of premium grade, deionized water is of analytical grade, the purity of anhydrous ethanol is ≥99.7 wt%, and the purity of N,N-dimethylformamide is ≥99.5 wt%.

3. The method for preparing the cobalt-based metal organic framework derivative absorber having a nanocomposite structure according to claim 1, characterized in that: The amount of cobalt nitrate hexahydrate was 1.748 g, the amount of terephthalic acid was 0.6 g, the amount of polyvinylpyrrolidone K30 was 4.0 g, and the amounts of deionized water, anhydrous ethanol, and N,N-dimethylformamide were each 40 mL.

4. The method for preparing the cobalt-based metal organic framework derivative absorber having a nanocomposite structure according to claim 1, characterized in that: The stirring time is 20 to 40 minutes, and the solvent thermal reaction condition is to keep the temperature at 180 to 220° C. for 10 to 15 hours.

5. The method for preparing the cobalt-based metal organic framework derivative absorber having a nanocomposite structure according to claim 1, characterized in that: The drying conditions are vacuum drying at 50-70°C for 6-10 hours.

6. The method for preparing the cobalt-based metal organic framework derivative absorber having a nanocomposite structure according to claim 1, characterized in that: The process parameters of high-temperature carbonization in the tube furnace are: heating rate of 8-12 °C / min, holding temperature of 700 °C±10 °C, holding time of 4-6 hours; and protective atmosphere of a mixed gas of 95% Ar and 5% H2 by volume.

7. An application of the method for preparing a cobalt-based metal organic framework derivative absorber having a nanocomposite structure according to any one of claims 1 to 6, characterized in that: The cobalt-based metal organic framework derivative is used as a wave absorbing material in the frequency band between 11 and 18 GHz.

8. Use of the method for preparing the cobalt-based metal organic framework derivative absorber having a nanocomposite structure according to claim 7, characterized in that: A cobalt-based metal-organic framework derivative is mixed with a medium that absorbs electromagnetic waves to serve as an absorbing material; based on mass percentage, the cobalt-based metal-organic framework derivative comprises 30 wt. % to 60 wt. %, and the rest is the medium that absorbs electromagnetic waves.

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