Preparation method of MOF-based multi-phase composite electromagnetic wave absorbing material

Abstract

A method for preparing a MOF-based multiphase composite electromagnetic wave absorbing material is disclosed, which relates to the preparation method and application of electromagnetic wave absorbing materials. The purpose of this invention is to solve the problems of poor attenuation and narrow absorption bandwidth in ABO3-type perovskite electromagnetic wave absorbing materials prepared by existing methods. This invention is based on the metallic Fe in MIL-88A. 3+ Ions were successfully induced to form an oxide perovskite phase in MIL-88A via etching, resulting in a hierarchical hollow nanocomposite material. In this structure, the oxide perovskite, a typical spinel-type p-type semiconductor, is composited with the surrounding elemental Fe phase through an outer graphitized carbon shell. Utilizing the heterojunction effect with metal-semiconductor contacts, an excellent interfacial polarization process is generated, significantly enhancing the dielectric loss performance of the composite material. Simultaneously, by consuming excess Fe metal... 3+ Excellent electromagnetic wave absorption performance was obtained by adjusting the impedance matching of the composite material.

Description

Technical Field

[0001] This invention relates to a method for preparing electromagnetic wave absorbing materials and their applications. Background Technology

[0002] With the rapid development of science and technology, people have invented various electronic microwave devices and widely applied them in various fields of military and daily life. At the same time, the complex electromagnetic environment generated by the operation of these electronic microwave devices has also brought many negative impacts to people's lives. For example, during operation, they will more or less radiate electromagnetic waves, which can harm the human body or interfere with other precision instruments and equipment. In the military, with the iterative development of reconnaissance equipment such as radar, the detection and destruction of targets has become possible. Currently, electromagnetic radiation pollution has become the fourth major public hazard threatening human survival, following air pollution, noise pollution, and water pollution. As people's technological level continues to improve, while pursuing a high quality of life, they inevitably face electromagnetic radiation.

[0003] Therefore, the research and application of electromagnetic absorbing materials to reduce electromagnetic pollution have gradually attracted the attention of scholars. Currently, absorbing materials are widely used in stealth technology and human protection. Among them, metal-organic framework (MOF) materials are increasingly widely used in electromagnetic wave absorption due to their simple preparation, superior performance, and lack of secondary electromagnetic pollution. However, MOF materials composed of single metal nodes generally have poor absorption performance after sintering. In recent years, oxide perovskite materials have also been gradually applied in the field of electromagnetic absorption due to their better dielectric properties. However, to obtain higher absorption performance, oxide perovskite materials generally need to be doped or composited, and the prepared electromagnetic absorbing materials still suffer from poor attenuation and narrow absorption bandwidth. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of poor attenuation effect and narrow absorption bandwidth of ABO3 type perovskite electromagnetic absorbing materials prepared by existing methods, and to provide a method for preparing MOF-based multiphase composite electromagnetic wave absorbing materials.

[0005] This invention addresses the technical problems of poor attenuation and narrow absorption bandwidth in current electromagnetic absorbing materials. It innovatively selects magnetic metal as the metal node and uses an etching method to simultaneously introduce oxide perovskite phase into MOF material to obtain excellent impedance matching, improve the absorption performance of composite material, and obtain high-performance electromagnetic absorbing composite material.

[0006] A method for preparing a MOF-based multiphase composite electromagnetic wave absorbing material is specifically carried out according to the following steps:

[0007] I. Preparation of MOF matrix:

[0008] ① Dissolve the iron salt in deionized water to obtain an iron salt solution;

[0009] ② Dissolve fumaric acid in deionized water to obtain a fumaric acid solution;

[0010] ③ Mix the iron salt solution and the fumaric acid solution and stir to obtain a mixed solution; subject the mixed solution to a hydrothermal reaction to obtain the reaction product; wash the reaction product and then vacuum dry it to obtain the MOF matrix;

[0011] II. Preparation of MOF-based composite materials with external double precipitation:

[0012] ① Dissolve salt A and urea in deionized water to obtain mixed solution I;

[0013] ② Disperse the MOF matrix in anhydrous ethanol to obtain mixed solution II;

[0014] ③ Mix mixed solution I and mixed solution II evenly, then reflux in an oil bath at 80℃~90℃ to collect the precipitate; wash the precipitate with deionized water, and then vacuum dry to obtain the MOF-based composite material with double precipitate coating.

[0015] III. High-temperature annealing:

[0016] The MOF-based composite material with double precipitation on the outside is heated to 650℃~750℃ and then kept at 650℃~750℃ for a period of time to obtain a hierarchical hollow nanocomposite material with internal ABO3 phase, which is the MOF-based multiphase composite electromagnetic wave absorbing material.

[0017] The principle of this invention:

[0018] The purpose of this invention is to replace the B-site elements inside the MOF by adding A-site elements (La, Bi, Sm, etc.) under alkaline conditions and spontaneously exchanging cations with the MOF material. Then, through a co-precipitation process, the doped A-site metal element and the B-site element in the matrix form a double hydroxide precipitate, which is attached to the outside of the matrix. After subsequent high-temperature annealing, the perovskite phase is spontaneously assembled in the MOF material. Through the interaction between the derived perovskite phase and the internal metal element, the dielectric loss of the material is enhanced, thereby obtaining better absorption performance. Moreover, the synthesized material exists in a fine powder state, which has the characteristics of controllable morphology, simple synthesis, pollution-free synthesis process, and excellent performance.

[0019] The microstructure of the MOF-based multiphase composite electromagnetic wave absorbing material prepared by this invention is a polyhedral structure with an average grain length of about 3-5 μm and a diameter of 200-500 nm; wherein the perovskite phase accounts for 15%-30% of the total mass of the composite material.

[0020] This invention utilizes the perovskite phase, which acts as a semiconductor, to modulate the dielectric and magnetic losses of the matrix MOF material. By leveraging multiphase interactions, it obtains electromagnetic wave absorbing materials with high absorption intensity in the C-band (i.e., MOF-based multiphase composite electromagnetic wave absorbing materials).

[0021] Compared with existing technologies for improving the microwave absorption performance of MOF materials, the advantages of this invention are:

[0022] After derivatization of the perovskite phase, the electromagnetic wave absorption intensity is significantly superior to that of the matrix, and the preparation process is simple. The resulting material is a powder with small and uniform grain size and controllable shape. The coupling interaction between the metal, carbon layer, and semiconductor effectively improves the dielectric loss of the material, and the synthesis process emits no harmful gases. The material has a high degree of crystallinity, stable structure, and excellent absorption performance in the low-frequency range. Attached Figure Description

[0023] Figure 1 The figures show X-ray diffraction patterns, where a represents the annealed MIL-88A prepared in Example 1, and b represents the MOF-based multiphase composite electromagnetic wave absorbing material prepared in step three of Example 2.

[0024] Figure 2 The images are SEM images; in the figures, a is the SEM image of MIL-88A prepared in Example 1 before annealing, b is the SEM image of MIL-88A prepared in Example 1 after annealing, c is the SEM image of the MOF material with double precipitation coating prepared in step two of Example 2, and d is the SEM image of the MOF-based multiphase composite electromagnetic wave absorbing material prepared in step three of Example 2.

[0025] Figure 3 This is a transmission electron microscope image of the MOF-based multiphase composite electromagnetic wave absorbing material prepared in step three of Example 2;

[0026] Figure 4 The dielectric constant curves of MIL-88A prepared in Example 1 and MOF-based multiphase composite electromagnetic wave absorbing material prepared in step 3 of Example 2 are shown in the frequency range of 2 to 18 GHz. In the figure, (a) is the real part of the dielectric constant of MIL-88A and MOF-based multiphase composite electromagnetic wave absorbing material, and (b) is the imaginary part of the dielectric constant of MIL-88A and MOF-based multiphase composite electromagnetic wave absorbing material.

[0027] Figure 5 The permeability curves of MIL-88A prepared in Example 1 and MOF-based multiphase composite electromagnetic wave absorbing material prepared in step 3 of Example 2 are shown in the frequency range of 2 to 18 GHz. In the figure, (a) is the real part of the permeability of MIL-88A and MOF-based multiphase composite electromagnetic wave absorbing material, and (b) is the imaginary part of the permeability of MIL-88A and MOF-based multiphase composite electromagnetic wave absorbing material.

[0028] Figure 6 The figures show the reflection loss curves of MIL-88A prepared in Example 1 and the MOF-based multiphase composite electromagnetic wave absorbing material prepared in step three of Example 2 at specific thicknesses. The left figure represents MIL-88A, and the right figure represents the MOF-based multiphase composite electromagnetic wave absorbing material. The thicknesses of the curves in the left figure are 2.0 mm, 2.5 mm, 3.0 mm, 3.5 mm, 4.0 mm, 4.5 mm, and 5.0 mm, respectively. The thicknesses of the curves in the right figure are 2.0 mm, 2.5 mm, 3.0 mm, 3.5 mm, 4.16 mm, 4.5 mm, and 5.0 mm, respectively. Detailed Implementation

[0029] Specific Implementation Method 1: This implementation method describes a method for preparing a MOF-based multiphase composite electromagnetic wave absorbing material, which is specifically completed according to the following steps:

[0030] I. Preparation of MOF matrix:

[0031] ① Dissolve the iron salt in deionized water to obtain an iron salt solution;

[0032] ② Dissolve fumaric acid in deionized water to obtain a fumaric acid solution;

[0033] ③ Mix the iron salt solution and the fumaric acid solution and stir to obtain a mixed solution; subject the mixed solution to a hydrothermal reaction to obtain the reaction product; wash the reaction product and then vacuum dry it to obtain the MOF matrix;

[0034] II. Preparation of MOF-based composite materials with external double precipitation:

[0035] ① Dissolve salt A and urea in deionized water to obtain mixed solution I;

[0036] ② Disperse the MOF matrix in anhydrous ethanol to obtain mixed solution II;

[0037] ③ Mix mixed solution I and mixed solution II evenly, then reflux in an oil bath at 80℃~90℃ to collect the precipitate; wash the precipitate with deionized water, and then vacuum dry to obtain the MOF-based composite material with double precipitate coating.

[0038] III. High-temperature annealing:

[0039] The MOF-based composite material with double precipitation on the outside is heated to 650℃~750℃ and then kept at 650℃~750℃ for a period of time to obtain a hierarchical hollow nanocomposite material with internal ABO3 phase, which is the MOF-based multiphase composite electromagnetic wave absorbing material.

[0040] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that: the iron salt mentioned in step one ① is ferric nitrate hydrate, ferric sulfate hydrate, or ferric chloride; the ratio of the amount of iron salt to the volume of deionized water in step one ① is (0.3mol~0.5mol):(20mL~40mL). The other steps are the same as in Specific Implementation Method One.

[0041] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that: in step 1, ②, fumaric acid is dissolved in deionized water under water bath and ultrasonic conditions at 65℃~75℃ to obtain a fumaric acid solution; the volume ratio of fumaric acid to deionized water in step 1, ② is (0.7mol~0.9mol):(60mL~80mL). Other steps are the same as in Specific Implementation Method 1 or 2.

[0042] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that: the volume ratio of the iron salt solution to the fumaric acid solution in step one ③ is (20mL~40mL):(60mL~80mL); the stirring time in step one ③ is 10min~20min. Other steps are the same as in Specific Implementation Methods One to Three.

[0043] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that: the hydrothermal reaction temperature in step one ③ is 110℃~120℃, and the hydrothermal reaction time is 10h~12h; in step one ③, the reaction product is centrifuged and washed 3 to 5 times with anhydrous ethanol and deionized water respectively, and then vacuum dried at 60℃~70℃ for 10h~12h to obtain the MOF matrix. Other steps are the same as in Specific Implementation Methods One to Four.

[0044] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that: the salt A mentioned in step two ① is La(NO3)3·6H2O, Bi(NO3)3·5H2O, or Sm(NO3)3·6H2O; the mass ratio of salt A to urea in step two ① is 1:1; the mass ratio of salt A to deionized water in step two ① is 1g:(20mL~40mL). Other steps are the same as in Specific Implementation Methods One to Five.

[0045] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that: the mass ratio of the MOF matrix to salt A in step two ② is (500mg~600mg):1g; the mass ratio of the MOF matrix to anhydrous ethanol in step two ② is (500mg~600mg):(20mL~40mL). The other steps are the same as in Specific Implementation Methods One to Six.

[0046] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that: the volume ratio of mixed solution I and mixed solution II in step two ③ is 1:1; the reflux time in step two ③ is 3 to 5 hours; in step two ③, the precipitate is washed 3 to 5 times with deionized water, and then vacuum dried at 60°C to 70°C for 10 to 12 hours to obtain the MOF material with double precipitate coating. Other steps are the same as in Specific Implementation Methods One to Seven.

[0047] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that: the heating rate in step three is 3℃ / min to 5℃ / min; the holding time in step three is 150min to 180min. Other steps are the same as in Specific Implementation Methods One to Eight.

[0048] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that: a MOF-based multiphase composite electromagnetic wave absorbing material is used as the electromagnetic wave absorbing material. The other steps are the same as in Specific Implementation Methods One to Nine.

[0049] The beneficial effects of the present invention are verified using the following embodiments:

[0050] Example 1: The preparation of the MOF matrix was carried out according to the following steps:

[0051] ① Dissolve 0.4 mol Fe(NO3)3·9H2O in 30 mL of deionized water to obtain an iron salt solution;

[0052] ② Dissolve 0.8 mol of fumaric acid in 70 mL of deionized water under water bath and ultrasonic conditions at 65℃ to obtain a fumaric acid solution;

[0053] ③ Mix the iron salt solution and the fumaric acid solution and stir for 10 min to obtain a mixed solution; subject the mixed solution to a hydrothermal reaction at 110℃ for 12 h to obtain the reaction product; wash the reaction product by centrifugation three times with anhydrous ethanol and deionized water respectively, and then vacuum dry at 60℃ for 12 h to obtain MIL-88A, which is the MOF matrix.

[0054] Example 2: A method for preparing a MOF-based multiphase composite electromagnetic wave absorbing material, which is carried out according to the following steps:

[0055] I. Preparation of MOF-based composite materials with external double precipitation:

[0056] ① Dissolve 1g of La(NO3)3·6H2O and 1g of urea in 30mL of deionized water to obtain mixed solution I;

[0057] ② Disperse 600 mg of the MOF matrix prepared in Example 1 into 30 mL of anhydrous ethanol to obtain mixed solution II;

[0058] ③ Mix mixed solution I and mixed solution II evenly, then reflux in an oil bath at 90℃ for 4 hours and collect the precipitate; wash the precipitate three times with deionized water, and then vacuum dry at 60℃ for 12 hours to obtain MOF material with double precipitate coating.

[0059] II. High-temperature annealing:

[0060] The MOF material with double precipitation coating was heated to 700℃ at a heating rate of 5℃ / min, and then held at 700℃ for 180min to obtain MOF-based multiphase composite electromagnetic wave absorbing material (LFO-1).

[0061] The MOF matrix prepared in Example 1 was placed in a tube furnace and heated to 700°C at a rate of 5°C / min, and then held at 700°C for 180 min to obtain annealed MIL-88A (LFO-0).

[0062] Figure 1 The figures show X-ray diffraction patterns, where a represents the annealed MIL-88A prepared in Example 1, and b represents the MOF-based multiphase composite electromagnetic wave absorbing material prepared in step three of Example 2.

[0063] Depend on Figure 1 (a) It can be seen that after annealing at 700℃, MIL-88A exhibits obvious Fe diffraction peaks, with a high-intensity Fe elemental peak at 44°, proving that after high-temperature annealing, most of the Fe in MIL-88A is absorbed by Fe. 3+ It is reduced to Fe by carbon. Figure 1 (b) It can be seen that after the double precipitation process, a small portion of Fe from LFO-1 was lost. 3+ The B-site elements that make up the perovskite phase mostly exist in elemental form. They will play a significant role in the synergistic microwave loss of the multiphase structure, providing magnetic loss for the absorber. Multiple diffraction peaks at 22°, 32°, and 57° match the standard card for LaFeO3, demonstrating that LaFeO3 was successfully derived into the MIL-88A matrix through alkaline co-precipitation and subsequent annealing.

[0064] Figure 2 The images are scanning electron microscope (SEM) images; in the figure, a is the SEM image of MIL-88A prepared in Example 1 before annealing, b is the SEM image of MIL-88A prepared in Example 1 after annealing, c is the SEM image of the MOF-based composite material with external double precipitation prepared in step two of Example 2, and d is the SEM image of the MOF-based multiphase composite electromagnetic wave absorbing material prepared in step three of Example 2.

[0065] from Figure 2 It can be seen that the MOF matrix material has an 18-sided prismatic structure, approximately 2 μm in length and 300 nm in diameter, with a smooth surface and intact structure. (See details...) Figure 2 (a);

[0066] The overall structure of LFO-1 remained largely unchanged, with externally attached double hydroxide precipitates serving as the base material for the derived perovskite phase. (See details...) Figure 2 (c);

[0067] The overall structure of LFO-1 did not change significantly after annealing; see details below. Figure 2 (d);

[0068] The microstructure of LFO-1 was further analyzed using transmission electron microscopy. Figure 3 (ac) shows that after annealing, MIL-88A exhibits a multiphase structure with uneven size. High-resolution TEM image analysis reveals that these phases are the (112) crystal plane of the LaFeO3 phase with a lattice stripe width of 0.279 nm. See details... Figure 3 (e) The (110) crystal plane of the Fe elemental phase with a lattice stripe width of 0.203 nm, see details. Figure 3 (f) Consistent with XRD analysis results, this demonstrates the successful derivation of the LaFeO3 phase within MIL-88A after high-temperature annealing. Simultaneously, the abundant interfaces resulting from the multiphase structure lead to strong interfacial polarization, significantly enhancing the material's dielectric loss and contributing to impedance matching balance, thereby improving microwave absorption performance.

[0069] Annealed MIL-88A (LFO-0) was mixed with paraffin wax at a mass ratio of 4:6 until homogeneous. A small amount of cyclohexane was then added and mixed evenly at 70°C. After drying, the mixture was pressed into paraffin rings with an inner diameter of 3.04 mm, an outer diameter of 7 mm, and a thickness of 2 mm using a mold to obtain the microwave absorber. The electromagnetic properties of the microwave absorber were tested, see [see details]. Figures 4-6 As shown in (a);

[0070] The MOF-based multiphase composite electromagnetic wave absorbing material (LFO-1) prepared in Example 2 was mixed with paraffin at a mass ratio of 4:6. A small amount of cyclohexane was then added and the mixture was uniformly mixed at 70°C. After drying, the mixture was pressed into paraffin rings with an inner diameter of 3.04 mm, an outer diameter of 7 mm, and a thickness of 2 mm using a mold to obtain the microwave absorber. The electromagnetic properties of the microwave absorber were tested, see [see details]. Figures 4-6 As shown in (b);

[0071] The dielectric constant curves of the microwave absorber at frequencies from 2 to 18 GHz, measured using a vector network analyzer, are shown below. Figure 4 As shown;

[0072] Figure 4The dielectric constant curves of MIL-88A prepared in Example 1 and MOF-based multiphase composite electromagnetic wave absorbing material prepared in step 3 of Example 2 are shown in the frequency range of 2 to 18 GHz. In the figure, (a) is the real part of the dielectric constant of MIL-88A and MOF-based multiphase composite electromagnetic wave absorbing material, and (b) is the imaginary part of the dielectric constant of MIL-88A and MOF-based multiphase composite electromagnetic wave absorbing material.

[0073] Depend on Figure 4 It can be seen that after LFO-1 undergoes alkaline precipitation and high-temperature annealing to derive the LaFeO3 phase, its P-type semiconductor generates a stronger interfacial polarization process through the interaction between the external carbon layer and the metal element, thus possessing the highest real and imaginary dielectric parts.

[0074] The real and imaginary parts of the dielectric constant of LFO-0 are both lower than those of LFO-1. This is because MIL-88A did not undergo the subsequent alkaline precipitation process. After high-temperature annealing, the internal phase of the structure is simple, and the microscopic processes that provide dielectric properties, such as polarization and relaxation, are not obvious. Therefore, it has a lower real and imaginary part of the dielectric constant.

[0075] The permeability curves of the absorbing agent at frequencies of 2–18 GHz were obtained using a vector network analyzer, as shown below. Figure 5 As shown;

[0076] Figure 5 The permeability curves of MIL-88A prepared in Example 1 and MOF-based multiphase composite electromagnetic wave absorbing material prepared in step 3 of Example 2 are shown in the frequency range of 2 to 18 GHz. In the figure, (a) is the real part of the permeability of MIL-88A and MOF-based multiphase composite electromagnetic wave absorbing material, and (b) is the imaginary part of the permeability of MIL-88A and MOF-based multiphase composite electromagnetic wave absorbing material.

[0077] Depend on Figure 5 It can be seen that the perovskite phase derivation results in a decrease in both the real and imaginary parts of the magnetic permeability compared to the original MIL-88A matrix. This is due to the large amount of Fe inside the material. 3+ As the B-site element becomes LaFeO3, the amount of elemental Fe reduced by annealing decreases, thus reducing its magnetic properties.

[0078] Compared to traditional methods for improving MOF (Metal-Oxide-Factory) absorbing materials, which involve altering the ratio of organic ligands to metal nodes to control impedance matching or combining them with other materials to enhance absorption, this invention utilizes the metal nodes provided by the MOF material itself to combine with desired perovskite A-site elements. Through high-temperature annealing, a new phase spontaneously arises within the perovskite. Depending on the requirements, suitable perovskite materials can be selected to address performance deficiencies in the MOF matrix material, while simultaneously balancing impedance matching to achieve the optimal absorption performance.

[0079] The absorption performance of absorbing materials of different thicknesses in the frequency range of 2-18GHz is as follows: Figure 6 As shown; compared to the MIL-88A substrate with poor absorption performance (see left image), by Figure 6 As shown in the right-hand figure, the absorption peak of the material after the derivation of the perovskite phase is centered at 6.32 GHz, and the lowest reflection loss reaches -68.1 dB, effectively enhancing its performance compared to the original MOF matrix. This is due to the material's unique multiphase blended hierarchical hollow nanocomposite structure. In this structure, LaFeO3, as a typical spinel-type p-type semiconductor, combines with the surrounding Fe elemental phase through an outer graphitized carbon shell, generating a special heterojunction effect with metal-semiconductor contacts. Furthermore, the work function of LaFeO3 is 4.93 eV, which is greater than the work function of Fe elemental phase (4.5 eV), i.e., W... m <W s When LaFeO3 / C / Fe come into contact, a special Schottky contact will form at the interface. Electrons will flow from Fe to the LaFeO3 surface. The Fe surface is positively charged, and the LaFeO3 surface is negatively charged, creating a negative space charge region at the contact surface. The electric field direction is from the outside to the inside, creating a potential difference between the inside and outside, with the surface potential V. s When the electron density is less than 0, the bandgap bends downwards. Because the surface electron concentration is much higher than the bulk electron concentration, a high-resistivity region is formed, which greatly increases conduction loss and effectively enhances the dielectric loss of the material, thus significantly improving its microwave absorption performance.

[0080] The preparation process of this invention is simple and the synthesis process is safe and pollution-free. The dielectric loss of the obtained microwave absorbing material is significantly improved compared with the original MOF matrix, and the magnetic loss is also balanced. This provides a reference for MOFs to derive various perovskite phases to regulate the microwave absorbing performance of the matrix.

Claims

1. A method for preparing a MOF-based heterogeneous composite electromagnetic wave absorbing material, characterized in that The preparation method is specifically carried out according to the following steps: I. Preparation of MOF matrix: ① Dissolve the iron salt in deionized water to obtain an iron salt solution; ② Dissolve fumaric acid in deionized water to obtain a fumaric acid solution; ③ Mix the iron salt solution and the fumaric acid solution and stir to obtain a mixed solution; subject the mixed solution to a hydrothermal reaction to obtain the reaction product; wash the reaction product and then vacuum dry it to obtain the MOF matrix; II. Preparation of MOF-based composite materials with external double precipitation: ① Dissolve salt A and urea in deionized water to obtain mixed solution I; The salt A mentioned in step 2① is La(NO3)3·6H2O or Sm(NO3)3·6H2O; ② Disperse the MOF matrix in anhydrous ethanol to obtain mixed solution II; ③ Mix mixed solution I and mixed solution II evenly, then reflux in an oil bath at 80℃~90℃ to collect the precipitate; wash the precipitate with deionized water, and then vacuum dry to obtain the MOF-based composite material with double precipitate coating. III. High-temperature annealing: The outer coated double-deposited MOF-based composite material is heated to 650 DEG C ~ 750 DEG C, and then is kept at 650 DEG C ~ 750 DEG C for a period of time, so that a hierarchical hollow nanocomposite material with an internally derived ABO3 phase is obtained, wherein the B element in ABO3 is Fe 3+ , which is a MOF-based multi-phase composite electromagnetic wave absorbing material.

2. The preparation method of the MOF-based multi-phase composite electromagnetic wave absorbing material according to claim 1, characterized in that The iron salt mentioned in step 1① is ferric nitrate hydrate, ferric sulfate hydrate, or ferric chloride; the molar ratio of the iron salt mentioned in step 1① to the volume ratio of deionized water is (0.3mol~0.5mol):(20mL~40mL).

3. The method for preparing a MOF-based multi-phase composite electromagnetic wave absorbing material according to claim 1, characterized in that In step 1②, fumaric acid is dissolved in deionized water under water bath and ultrasonic conditions at 65℃~75℃ to obtain fumaric acid solution; the molar ratio of fumaric acid to deionized water in step 1② is (0.7mol~0.9mol):(60mL~80mL).

4. The method for preparing a MOF-based multiphase composite electromagnetic wave absorbing material according to claim 1, characterized in that... The volume ratio of the iron salt solution to the fumaric acid solution mentioned in step 1 ③ is (20 mL ~ 40 mL): (60 mL ~ 80 mL); the stirring time mentioned in step 1 ③ is 10 min ~ 20 min.

5. The method for preparing a MOF-based multiphase composite electromagnetic wave absorbing material according to claim 1, characterized in that... The hydrothermal reaction temperature in step 1, section 3 is 110℃~120℃, and the hydrothermal reaction time is 10h~12h. In step 1, section 3, the reaction product is centrifuged and washed 3 to 5 times with anhydrous ethanol and deionized water respectively, and then vacuum dried at 60℃~70℃ for 10h~12h to obtain the MOF matrix.

6. The method for preparing a MOF-based multiphase composite electromagnetic wave absorbing material according to claim 1, characterized in that... The mass ratio of salt A to urea in step 2① is 1:1; the mass ratio of salt A to deionized water in step 2① is 1g:(20mL~40mL).

7. The method for preparing a MOF-based multiphase composite electromagnetic wave absorbing material according to claim 1, characterized in that... The mass ratio of MOF matrix to salt A in step 2② is (500mg~600mg):1g; the mass ratio of MOF matrix to anhydrous ethanol in step 2② is (500mg~600mg):(20mL~40mL).

8. The method for preparing a MOF-based multiphase composite electromagnetic wave absorbing material according to claim 1, characterized in that... The volume ratio of mixed solution I and mixed solution II in step 2③ is 1:1; the reflux time in step 2③ is 3h~5h; in step 2③, the precipitate is washed with deionized water 3~5 times, and then vacuum dried at 60℃~70℃ for 10h~12h to obtain the MOF material with double precipitation coating.

9. The method for preparing a MOF-based multiphase composite electromagnetic wave absorbing material according to claim 1, characterized in that... The heating rate mentioned in step three is 3℃ / min to 5℃ / min; the holding time mentioned in step three is 150min to 180min.

10. The method for preparing a MOF-based multiphase composite electromagnetic wave absorbing material according to claim 1, characterized in that... A MOF-based multiphase composite electromagnetic wave absorbing material is used as an electromagnetic wave absorbing material.

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