CN113620349B - One-dimensional iron-based wave-absorbing material derived from metal organic framework and preparation method thereof - Google Patents

Abstract

The invention discloses a one-dimensional iron-based wave-absorbing material derived from a metal organic framework and a preparation method thereof, belonging to the technical field of microwave absorbing materials. A one-dimensional metal organic framework (Fe-bdc) is used as a precursor, and the processes of air oxidation and hydrogen reduction are adopted, so that the regulation and control of the content and the morphology of magnetic components in the derived one-dimensional iron-based wave-absorbing material are realized, the optimization of electromagnetic parameters is promoted, and the effective absorption of broadband electromagnetic waves is realized under low thickness. From the aspect of composition, the oxidation process effectively removes non-magnetic components, and the reduction process effectively adjusts the content of each magnetic component. From the structure, the one-dimensional continuous bead-shaped structure has stronger shape anisotropy, can promote the formation of magnetic conduction and electric conduction paths, and is beneficial to the enhancement of the electromagnetic attenuation capability. The effective absorption frequency band of the one-dimensional iron-based wave-absorbing material can reach 3.52 GHz when the thickness is only 1.2 mm, and the one-dimensional iron-based wave-absorbing material shows excellent low-thickness broadband wave-absorbing characteristics. The process does not need complex equipment, has low cost and strong product consistency.

Description

One-dimensional iron-based wave absorbing material derived from metal organic framework and preparation method thereof

technical field

The invention belongs to the technical field of microwave absorbing materials, and particularly relates to a one-dimensional iron-based wave absorbing material derived from a metal organic framework and a preparation method.

Background technique

The rapid development of 5G communication technology has greatly facilitated human life, but at the same time, it has also brought about increasingly serious electromagnetic pollution problems, and it is urgent to develop high-efficiency microwave absorbing materials. With the acceleration of the construction of small 5G base stations and the upgrading of a large number of microelectronic devices, wide effective absorption frequency bands and low thickness have gradually become the core goals of the research and development of absorbing materials. According to the electromagnetic theory, the reduction of the thickness of the absorbing material can be achieved by increasing the complex permittivity or the complex permeability. Among them, the introduction of the one-dimensional structure can effectively reduce the percolation threshold of the wave absorbing material in the wave-transmitting matrix, promote the formation of the conductive network, and then improve the complex permittivity. For example, Ding et al. prepared TiO ₂ nanowires by a solvothermal method, and then used a gas-phase polymerization process to prepare a one-dimensional TiO ₂ @Fe ₃ O ₄ @PPy coaxial composite material. The absorption band of this material at a thickness of 2.2 mm Up to 6 GHz, the peak reflection loss can reach -61.8 dB ( Small , 2019, 15). Interestingly, the one-dimensional structure can also cause changes in magnetic anisotropy, thereby affecting the complex permeability spectrum of the absorber. For example, Shen et al. successfully synthesized iron nanowires with a diameter of 100 nm by a magnetic field-assisted hydrothermal method. Compared with conventional iron nanowires, iron nanowires have higher saturation magnetization and coercivity, complex permeability There is also a corresponding increase ( Journal of Alloys and Compounds , 2016, 4). In addition, numerous studies have shown that the broadening of the effective absorption band is highly dependent on the increase of the complex permeability and the matching of the complex permittivity. Li et al. synthesized Fe ₂ O ₃ @PVP material by hydrothermal method, and formed Fe ₃ O ₄ -Fe@C core-shell material after heat treatment, in which magnetic Fe and Fe ₃ O ₄ provided strong magnetic loss, while Fe 3 O 4 -Fe@C core-shell material was formed after heat treatment The carbon shell greatly improves the dielectric loss capability of the material, allowing the material to meet the absorption requirements in the Ku-band at a thickness of 1.99 mm ( Journal of Alloys and Compounds , 2020, 821). Although researchers have overcome the problems of narrow effective absorption band and large matching thickness of some absorbing material products through many means, how to achieve effective absorption band broadening at lower matching thickness is still an urgent problem to be solved. At the same time, the simplification of the preparation process and the improvement of product uniformity are also the difficulties faced in the research and development of absorbing materials.

SUMMARY OF THE INVENTION

In order to take into account the broadening of the effective absorption band and the reduction of the matching thickness, the present invention provides a one-dimensional iron-based wave absorbing material derived from a metal organic framework, and a preparation method of the one-dimensional iron-based wave absorbing material derived from a metal organic framework.

A one-dimensional iron-based wave absorbing material derived from a metal-organic framework is gray-black powder, and the components include iron, ferric oxide, and ferrous oxide, wherein the mass fraction of iron is 47.3-63.79%; The particles are in the shape of one-dimensional contiguous beads, and the contiguous beads are cylindrical beads with a length of 300-2000 nm and a diameter of 20-1000 nm.

The preparation operation steps of a one-dimensional iron-based wave absorbing material derived from a metal organic framework are as follows:

(1) Dissolve 1.08 g of ferric chloride hexahydrate in 54 mL of N,N-dimethylformamide solution, stir for 10 min, then add 0.88 g of terephthalic acid, and stir for 30 min to obtain an iron salt solution; Another 0.096 g of sodium hydroxide was dissolved in 6 mL of deionized water, added to the iron salt solution, and solvothermally reacted at 100 °C for 24 h; the product was centrifuged and washed twice with N,N-dimethylformamide; Dry in a vacuum drying oven at a temperature of 80°C for 1 hour; grind to obtain a metal organic framework powder; the metal organic framework powder is pale yellow, with iron as the central metal element and terephthalic acid as the organic ligand, Denoted as Fe-bdc, the particles of the metal-organic framework powder are one-dimensional rods with a length of 1000 nm and a diameter of 100 nm;

(2) Take 1 g of the above metal-organic framework powder, heat treatment in a muffle furnace under air conditions, raise the temperature to 450-650 °C at 2 °C/min, hold for 4 h, naturally cool, and grind to obtain a metal-organic framework derivative. Iron oxide powder, the metal-organic framework-derived iron oxide powder is red, the powder particles are rod-shaped, the rod length is 300-1000 nm, and the diameter is 20-100 nm;

(3) Take 0.5 g of the above metal-organic framework-derived iron oxide powder, reduce it in a hydrogen atmosphere in a tube furnace, raise it to 350-550 °C at 2 °C/min, keep it for 1 h, cool it naturally, and grind it to get A one-dimensional iron-based wave absorbing material derived from a metal-organic framework; the one-dimensional iron-based wave absorbing material is gray-black powder, and the components mainly include iron, iron tetroxide, and ferrous oxide, wherein the mass fraction of iron is 47.3~ 63.79 %; the powder particles are one-dimensional contiguous beads, and the contiguous beads are cylindrical beads with a length of 300-2000 nm and a diameter of 20-1000 nm.

The beneficial technical effect of the present invention is embodied in the following aspects:

1. In the present invention, the metal organic framework is used as the precursor, and the one-dimensional iron-based composite wave absorbing material is obtained by the method of first oxidation and then reduction. Among them, changing the redox conditions can realize the effective control of the magnetic metal composition, content and morphology in the derivative iron-based absorbing material, which promotes the increase and optimization of the complex permeability and complex permittivity, and then realizes the low-thickness Broadening of the effective absorption band. In terms of composition, the organic components were completely removed after the oxidation of the precursor rod-shaped Fe-bdc, which ensured a high content of magnetic components after reduction. The controllable hydrogen reduction realizes the adjustment of the reduction degree of iron oxide, and then realizes the change of the content of iron and its oxides in the product, thereby adjusting the electromagnetic parameters. From a structural point of view, after redox, the derivative products are in bead-like shape with strong shape anisotropy, which makes the material exhibit high complex magnetic permeability, and the small particle size of the product effectively limits the eddy current effect. Improved absorbing performance in the high frequency range. Benefiting from the above advantages, the effective absorption frequency range of the derived one-dimensional iron-based absorber with a filling degree of 60 wt% and a thickness of 1.2 mm can reach 14.48-18 GHz; its reflection at 16.16 GHz with a thickness of 1.2 mm The peak loss can reach -43.77 dB, showing excellent low-matching thickness broadband absorbing performance.

2. The present invention uses solvothermally synthesized metal-organic framework Fe-bdc as the precursor, and has high yield and strong consistency. The oxidation and reduction processes are mature industrial production processes with strong controllability. The overall production process is simple, no complicated and expensive equipment is required, the production cost is low, the product consistency is strong, and large-scale production can be realized.

Description of drawings

Figure 1 is the SEM image of the as-prepared metal-organic framework Fe-bdc.

Figure 2 is the SEM photograph of the prepared metal-organic framework Fe-bdc-derived iron oxide.

FIG. 3 is an XRD pattern of the one-dimensional iron-based wave absorbing material S1 prepared in Example 1. FIG.

FIG. 4 is a SEM photograph of the one-dimensional iron-based wave absorbing material S1 prepared in Example 1. FIG.

FIG. 5 is the electromagnetic parameter spectrum of the one-dimensional iron-based wave absorbing material S1 prepared in Example 1. FIG.

FIG. 6 is a graph showing the reflection loss of the one-dimensional iron-based wave absorbing material S1 prepared in Example 1. FIG.

FIG. 7 is the XRD spectrum of the one-dimensional iron-based wave absorbing material S2 prepared in Example 2. FIG.

FIG. 8 is an SEM photograph of the one-dimensional iron-based wave absorbing material S2 prepared in Example 2. FIG.

FIG. 9 is the electromagnetic parameter spectrum of the one-dimensional iron-based wave absorbing material S2 prepared in Example 2. FIG.

FIG. 10 is a graph showing the reflection loss of the one-dimensional iron-based wave absorbing material S2 prepared in Example 2. FIG.

Detailed ways

The technical solutions of the present invention will be further described below with reference to the accompanying drawings.

Example 1

The specific preparation operation steps of a one-dimensional iron-based wave absorbing material derived from a metal organic framework are as follows:

(1) Dissolve 1.08 g of ferric chloride hexahydrate in 54 mL of N,N-dimethylformamide solution, stir for 10 min, then add 0.88 g of terephthalic acid, and stir for 30 min to obtain an iron salt solution; Another 0.096 g of sodium hydroxide was dissolved in 6 mL of deionized water, the sodium hydroxide solution was poured into the iron salt solution, and the solvothermal reaction was carried out at 100 °C for 24 h; - Washing twice with dimethylformamide, drying in a vacuum drying oven at a temperature of 80°C for 1 hour; grinding to obtain a metal organic framework powder; the metal organic framework powder is pale yellow, with iron as the central metal element, Taking terephthalic acid as the organic ligand, denoted as Fe-bdc, the particles of the metal-organic framework powder are one-dimensional rods with a length of 1000 nm and a diameter of about 100 nm.

(2) Take 1 g of the above metal organic framework powder, heat treatment in a muffle furnace under air conditions, raise the temperature to 550 °C at 2 °C/min, hold for 4 h, cool naturally, and grind to obtain metal organic framework-derived iron oxide. Powder, the metal-organic framework-derived iron oxide powder is red in color, and the powder particles are in the shape of rods with a rod length of 500 nm and a diameter of 50 nm.

(3) Take 0.5 g of the above-mentioned metal-organic framework-derived iron oxide powder, reduce it in a hydrogen atmosphere in a tube furnace, raise it to 350 °C at 2 °C/min, keep it for 1 h, cool it naturally, and grind it to obtain a metal-organic Frame-derived one-dimensional iron-based wave absorbing material; the one-dimensional iron-based wave absorbing material is gray-black powder, and the components include iron, iron tetroxide, and ferrous oxide, wherein the mass fraction of iron is 63.79%; powder particles It presents a one-dimensional concatenated bead shape, and the concatenated beads are cylindrical beads with a length of 1000 nm and a diameter of 100 nm.

Referring to FIG. 1 , the metal organic framework particles prepared in Example 1 have a one-dimensional rod-like structure, with a length of about 1000 nm and a diameter of about 100 nm.

Referring to FIG. 2 , the metal-organic framework-derived iron oxide powder particles prepared in Example 1 have a certain volume shrinkage after being oxidized at 450 °C, and some holes appear on the rod-shaped surface, but the overall one-dimensional rod-shaped structure is still maintained. The material is now about 500 nm long and 50 nm in diameter. Combined with the samples and the experimental process, the reason for this phenomenon is that the organic components in the material are oxidized and removed in the air, and the metal elements are oxidized to ferric oxide (Fe ₂ O ₃ ) in the air.

Referring to Fig. 3, the XRD spectrum of the one-dimensional iron-based wave absorbing material S1 prepared in Example 1 shows a number of obvious diffraction peaks, referring to the standard of ferric oxide (Fe ₃ O ₄ ). PDF card JCPDS No. 75-0033, the diffraction peaks in the figure correspond well to the characteristic peaks in the card, and there are no impurity peaks. Combined with the ICP test results, the iron content in the sample was 63.79 wt%, and the analysis showed that the S1 product was reduced by hydrogen to become ferric tetroxide (Fe ₃ O ₄ ) with high crystallinity.

Referring to FIG. 4 , the SEM photograph of the one-dimensional iron-based wave absorbing material S1 prepared in Example 1. It can be seen from the figure that the porous rod-like structure of the material changes into a one-dimensional structure of a bead-like structure after hydrogen reduction at 350 ^o C. The bead is a cylindrical bead with a length of about 1000 nm and a diameter of about 100 nm. The appearance of the one-dimensional bead-like structure is related to the reduction process of the material, that is, the ferric oxide (Fe ₃ O ₄ ) particles obtained by the reduction of ferric oxide (Fe ₂ O ₃ ) gradually grow up and connect with each other.

Referring to Fig. 5, the complex permittivity and complex permeability spectrum of the one-dimensional iron-based wave absorbing material S1 prepared in Example 1 with a filling degree of 60 wt%, from Fig. 5, the complex permittivity of S1 The constant varies from 23.72 at 2 GHz to 14.20 at 18 GHz, and the real part shows a clear downward trend in the range of 2-12 Ghz. The imaginary part of the complex permittivity shows a trend of rising first and then falling, with an obvious peak at 10 GHz, indicating that dielectric relaxation occurs at this time, which is beneficial to the enhancement of the polarization loss capability. This phenomenon may be caused by the existence of two valence states of iron (Fe) in ferric oxide (Fe ₃ O ₄ ), which greatly improves the dielectric loss capability of the material. The real part of the complex permeability and the imaginary part of the complex permeability of S1 decrease slowly with the increase of frequency as a whole. At 2 GHz, the real part of the complex permeability is about 1.65, and the imaginary part is about 0.50. There is a certain amount of rise in the real part around 10 GHz. The macroscopic appearance of one-dimensional beading of the material may be an important reason for the formation of the magnetic permeability path and the improvement of the complex magnetic permeability. In general, S1 has strong dielectric loss and magnetic loss capability at the same time.

Referring to Figure 6, the reflection loss curve of the one-dimensional iron-based wave absorbing material S1 prepared in Example 1 with a filling degree of 60 wt%, the material reflection loss peak at 1.2 mm thickness and 16.16 GHz can reach -43.76dB, and Effective absorption from 14.48-18 GHz is achieved. It can be seen that S1 has excellent absorbing properties at low thickness. The main component of the material is iron tetroxide (Fe ₃ O ₄ ), and it has excellent dielectric loss and magnetic loss ability. The one-dimensional bead-like structure is conducive to the formation of a magnetic permeability path, which improves the magnetic permeability of the material, thereby achieving superior impedance matching and magnetic loss capabilities.

Example 2

The specific preparation operation steps of a one-dimensional iron-based wave absorbing material derived from a metal organic framework are as follows:

(1) Dissolve 1.08 g of ferric chloride hexahydrate in 54 mL of N,N-dimethylformamide solution, stir for 10 min, then add 0.88 g of terephthalic acid, and stir for 30 min to obtain an iron salt solution; Another 0.096 g of sodium hydroxide was dissolved in 6 mL of deionized water, the sodium hydroxide solution was added to the iron salt solution, and the solvothermal reaction was carried out at 100 °C for 24 h; after the reaction, the product was centrifuged and separated with N,N- Washed twice with dimethylformamide; dried in a vacuum drying oven at 80°C for 1 hour; ground to obtain metal organic framework powder; the metal organic framework powder was pale yellow, with iron as the central metal element, with iron as the central metal element. Terephthalic acid is an organic ligand, denoted as Fe-bdc, and the particles of the metal-organic framework powder are one-dimensional rods with a length of 1000 nm and a diameter of about 100 nm.

(2) Take 1 g of the above metal organic framework powder, heat treatment in a muffle furnace under air conditions, increase to 450 °C at 2 °C/min, hold for 4 h, naturally cool, and grind to obtain metal organic framework-derived iron oxide. Powder, the metal-organic framework-derived iron oxide powder is red, and the powder particles are rod-shaped, with a length of 500 nm and a diameter of 50 nm;

(3) Take 0.5 g of the above-mentioned metal-organic framework-derived iron oxide powder, reduce it in a hydrogen atmosphere in a tube furnace, raise it to 550 °C at 2 °C/min, keep it for 1 h, cool it naturally, and grind it to obtain a metal organic Frame-derived one-dimensional iron-based wave absorbing material; the one-dimensional iron-based wave absorbing material is gray-black powder, and the components include iron, ferric oxide, and ferrous oxide, wherein the mass fraction of iron is 63.38%; powder particles It presents a one-dimensional concatenated bead shape, and the concatenated beads are cylindrical beads with a length of 2000 nm and a diameter of 500 nm.

Referring to FIG. 7 , the XRD spectrum of the one-dimensional iron-based wave absorbing material S2 prepared in Example 2. Three distinct diffraction peaks can be seen from Figure 7, corresponding to the (110), (200), (211) crystal planes of JCPDS No. 89-7194 Fe, respectively. Combined with the ICP test results, the iron content in this sample is 63.38 wt%, which is quite different from that of pure iron, indicating that under the action of hydrogen reduction at 550 ^o C, iron trioxide (Fe ₂ O ₃ ) is not only reduced to a better crystallinity In addition to the pure iron (Fe) phase, there may be some oxidation products in amorphous form.

Referring to Figure 8, the SEM photo of the one-dimensional iron-based wave absorbing material S2 prepared in Example 2, compared with S1, the one-dimensional beads in S2 adhered to each other, forming a conductive path; the particle size also changed from nanometers to micrometers level, about 2000 nm in length and 500 nm in diameter. The occurrence of this phenomenon may be caused by the high heat treatment temperature, which provides high energy to the material, resulting in faster grain growth.

Referring to FIG. 9 , the complex permittivity and complex permeability spectrum of the one-dimensional iron-based wave absorbing material S2 with a filling degree of 60 wt% prepared in Example 2. Compared with S1, the complex permittivity of S2 increased significantly, the real part increased from 23.72 of S1 to 77.74, and the imaginary part increased from 5.28 to 30.00. There is also a certain amount of increase in the complex permeability, but the overall change is not large. On the one hand, the obvious change of the parameters is because the material composition changes to a certain extent after the reduction temperature is increased, and the pure iron (Fe) phase has higher magnetic permeability and dielectric constant. On the other hand, from the morphology point of view, the particles in S2 are obviously interconnected, forming a conductive path, which further improves the conductive properties of the material.

Referring to FIG. 10 , the reflection loss curve of the one-dimensional iron-based wave absorbing material S2 with a filling degree of 60 wt % prepared in Example 2. The RL of the S2 samples are all greater than -10 dB, indicating that the material has poor absorbing performance. This is because at the same filling degree, the existence of pure iron (Fe) phase and conductive paths in S2 leads to a very high dielectric constant, which seriously affects the impedance matching ability of the material, so the reflection loss performance is poor.

Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be Included in the protection scope of the present invention.

Claims (1)

1. a one-dimensional iron-based wave absorbing material derived from a metal-organic framework, is characterized in that: The one-dimensional iron-based wave absorbing material is gray-black powder, and the components include iron, ferric oxide and ferrous oxide, wherein the mass fraction of iron element is 47.3-63.79%; the particles of the gray-black powder are one-dimensional continuous beads The connecting beads are cylindrical beads with a length of 300-2000 nm and a diameter of 20-1000 nm; The preparation operation steps of a one-dimensional iron-based wave absorbing material derived from a metal organic framework are as follows: (1) Dissolve 1.08 g of ferric chloride hexahydrate in 54 mL of N,N-dimethylformamide solution, stir for 10 min, then add 0.88 g of terephthalic acid, and stir for 30 min to obtain an iron salt solution; Another 0.096 g of sodium hydroxide was dissolved in 6 mL of deionized water, added to the iron salt solution, and solvothermally reacted at 100 °C for 24 h; the product was centrifuged and washed twice with N,N-dimethylformamide; Dry in a vacuum drying oven at a temperature of 80°C for 1 hour; grind to obtain a metal organic framework powder; the metal organic framework powder is pale yellow, with iron as the central metal element and terephthalic acid as the organic ligand, Denoted as Fe-bdc, the particles of the metal-organic framework powder are one-dimensional rods with a length of 1000 nm and a diameter of 100 nm; (2) Take 1 g of the above metal-organic framework powder, heat treatment in a muffle furnace under air conditions, raise the temperature to 450-650 °C at 2 °C/min, hold for 4 h, naturally cool, and grind to obtain a metal-organic framework derivative. Iron oxide powder, the metal-organic framework-derived iron oxide powder is red, the powder particles are rod-shaped, the rod length is 300-1000 nm, and the diameter is 20-100 nm; (3) Take 0.5 g of the above metal-organic framework-derived iron oxide powder, reduce it in a hydrogen atmosphere in a tube furnace, raise it to 350-550 °C at 2 °C/min, keep it for 1 h, cool it naturally, and grind it to get A one-dimensional iron-based wave absorbing material derived from a metal-organic framework; the one-dimensional iron-based wave absorbing material is gray-black powder, and the components include iron, ferric oxide, and ferrous oxide, wherein the mass fraction of iron is 47.3-63.79 %; the powder particles are in the shape of one-dimensional contiguous beads, and the contiguous beads are cylindrical beads with a length of 300-2000 nm and a diameter of 20-1000 nm.

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