MOF material and wave-absorbing material based on same

Abstract

The invention provides an MOF material, a wave-absorbing material based on the MOF material and a preparation method and application of the wave-absorbing material, and the preparation method comprises the following steps: mixing salt containing rare earth metal elements and magnetic metal elements, a linker and a solvent, and then sequentially carrying out pre-reaction and heating reaction to obtain the MOF material. And carrying out graphitization treatment on the obtained MOF material to obtain the wave-absorbing material. By improving a synthesis strategy and combining selection of rare earth metal, magnetic metal and a linker, the morphology and structure of the material can be regulated and controlled, so that the material has higher specific surface area and pore volume, meanwhile, the interaction opportunity of the wave-absorbing material and electromagnetic waves is increased, the wave-absorbing performance of the wave-absorbing material in the X wave band is improved, and the wave-absorbing material has good application prospects. And the requirements of light weight, wide frequency response and high absorption capability of the wave-absorbing material are met.

Description

Background Technology

[0001] With the rapid development of electronic information and communication technologies, the widespread application of electronic devices has led to a continuous increase in electromagnetic interference and pollution. To address this problem, microwave absorbing materials have become a research hotspot. Traditional microwave absorbing materials such as ferrites and metal powders have been extensively studied, but their irregular shapes limit their application range. Therefore, the search for novel microwave absorbing materials and the study of their preparation methods have become the focus of scientists' attention.

[0002] Metal-organic frameworks (MOFs) are ultraporous materials assembled from metal ions and organic ligands in suitable solvents. They exhibit variability in framework structure shape and functional groups, and their structures are influenced by many factors; different synthesis conditions may yield frameworks with different structures. Furthermore, MOFs possess extremely high specific surface areas, diverse structures, and tunable functionalities. Their porous structure effectively reflects electromagnetic waves, thus reducing electromagnetic wave attenuation, making them a subject of considerable interest.

[0003] MOF-derived carbon-based microwave absorbing materials have attracted increasing attention in electromagnetic wave absorption applications due to their diverse organic ligands, tunable chemical composition and graphitization degree, and porous structure. However, the preparation process of most MOF-derived carbon-based microwave absorbing materials is cumbersome, requires a large amount of energy, and the reflection loss still needs to be improved.

[0004] Therefore, developing a new composite microwave absorbing material based on MOF structure to solve the above problems, while simplifying the process and reducing production costs, is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to provide a composite microwave absorbing material based on MOF structure, its preparation method and application. The composite microwave absorbing material utilizes the electromagnetic resonance absorption mechanism and the excellent magnetic loss performance of magnetic materials. Rare earth metal elements and magnetic metal elements work synergistically to improve its microwave absorption performance in the X-band.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a composite microwave absorbing material based on a MOF structure, the method comprising the following steps:

[0008] (1) Salts containing rare earth metal elements, salts containing magnetic metal elements, linkers and solvents are mixed, and then pre-reaction and heating reaction are carried out in sequence to obtain MOF materials;

[0009] (2) The MOF material obtained in step (1) is graphitized to obtain a composite microwave absorbing material.

[0010] The preparation method provided by this invention, through improved synthesis strategy and selection of rare earth metals, magnetic metals and linkers, can control the morphology and structure of the material, giving it a higher specific surface area and pore volume. At the same time, it increases the interaction opportunities between the absorbing material and electromagnetic waves, improves its absorption performance in the X-band, and meets the requirements of lightweight, wide frequency response and high absorption capacity of absorbing materials.

[0011] As a preferred technical solution of the present invention, the rare earth metal element in step (1) includes any one of yttrium, lanthanum, cerium, praseodymium or neodymium.

[0012] Preferably, the magnetic metal element in step (1) includes any one of nickel, chromium, iron or cobalt.

[0013] It is worth noting that the composite absorbing material of this invention utilizes the synergistic effect of rare earth metal elements and magnetic metal elements, and leverages the electromagnetic resonance absorption mechanism and the excellent magnetic loss performance of magnetic materials to improve the absorption performance in the X-band.

[0014] Preferably, the salt in step (1) includes any one or a combination of at least two of nitrates, phosphates, sulfates, carbonates or chlorides.

[0015] Preferably, the molar ratio of the salt containing rare earth metal elements to the salt containing magnetic metal elements in step (1) is (0.8-1.2):1, for example, it can be 0.85:1, 0.9:1, 0.95:1, 1:1, 1.05:1, 1.1:1 or 1.15:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0016] As a preferred technical solution of the present invention, the linker in step (1) includes any one or a combination of at least two of isonicotinic acid (4-carboxypyridine), nicotinic acid, 2-aminoisonicotinic acid, methyl isonicotinic acid or ethyl isonicotinic acid. Typical but non-limiting combinations include: a combination of isonicotinic acid and nicotinic acid, a combination of 2-aminoisonicotinic acid and methyl isonicotinic acid, or a combination of methyl isonicotinic acid and ethyl isonicotinic acid, etc.

[0017] Preferably, the solvent in step (1) includes any one or a combination of at least two of N,N-dimethylformamide (DMF), methanol, ethanol or deionized water. Typical but not limited combinations include: a combination of DMF and methanol, a combination of DMF and ethanol, or a combination of DMF, methanol and deionized water, etc., preferably a combination of DMF, ethanol and deionized water.

[0018] In this invention, a mixed solution of DMF, ethanol and deionized water is used as a solvent, which helps metal ions to form coordination bonds with the linker and generate a porous spherical composite microwave absorbing material through coordination reaction.

[0019] Preferably, the molar ratio of the salt containing rare earth metal elements to the linker in step (1) is 1:(1-1.2), for example, it can be 1:1.02, 1:1.05, 1:1.07, 1:1.09, 1:1.1, 1:1.12, 1:1.12 or 1:1.15, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0020] As a preferred technical solution of the present invention, the pre-reaction in step (1) includes microwave heating.

[0021] Preferably, the power of the microwave heating is 360W.

[0022] Preferably, the microwave heating temperature is 50-70℃, for example, it can be 52℃, 54℃, 56℃, 58℃, 60℃, 62℃, 64℃, 66℃ or 68℃, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0023] Preferably, the microwave heating holding time is 2-4 minutes, for example, it can be 2.2 minutes, 2.5 minutes, 2.7 minutes, 3 minutes, 3.2 minutes, 3.5 minutes or 3.8 minutes, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] Preferably, the stirring is performed simultaneously with the microwave heating.

[0025] It is worth noting that microwave heating can rapidly improve the solubility and uniformity of reactants, effectively promoting the reaction process between metal ions and the linker; at the same time, stirring can ensure the full mixing and mass transfer of the reaction system, which can help accelerate the reaction.

[0026] As a preferred technical solution of the present invention, the heating reaction temperature in step (1) is 190-210℃, for example, it can be 192℃, 195℃, 197℃, 200℃, 202℃, 205℃ or 208℃, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] Preferably, the holding time for the heating reaction in step (1) is 28-32h, for example, it can be 28.5h, 29h, 29.5h, 30h, 30.5h, 31h or 31.5h, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] In this invention, the heating reaction in step (1) is carried out in a reaction vessel.

[0029] It is worth noting that the present invention involves heating the reaction at a specific temperature and holding it at that temperature for a period of time to promote crystal growth and the formation of a porous spherical structure.

[0030] As a preferred technical solution of the present invention, the heating reaction in step (1) further includes solid-liquid separation, washing and drying in sequence.

[0031] In this invention, the washing process includes washing at least three times with a mixed solution of DMF and deionized water.

[0032] Preferably, the drying temperature is 70-90℃, for example, it can be 72℃, 74℃, 76℃, 78℃, 80℃, 82℃, 84℃, 86℃ or 88℃, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0033] Preferably, the drying and heat preservation time is 10-14 hours, for example, it can be 10.5 hours, 11 hours, 11.5 hours, 12 hours, 12.5 hours, 13 hours or 13.5 hours, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] As a preferred technical solution of the present invention, the heating rate of the graphitization process in step (2) is 2-5℃ / min, for example, it can be 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min or 4.5℃ / min, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] In this invention, the graphitization process in step (2) is carried out in a tube furnace; the graphitization process is carried out in an argon atmosphere.

[0036] Preferably, the temperature of the graphitization process in step (2) is 750-850℃, for example, it can be 760℃, 770℃, 780℃, 790℃, 800℃, 810℃, 820℃, 830℃ or 840℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] Preferably, the heat preservation time for graphitization treatment in step (2) is 2-4h, for example, it can be 2.2h, 2.5h, 2.7h, 3h, 3.2h, 3.5h or 3.7h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0039] (1) Mix salts containing rare earth metal elements, salts containing magnetic metal elements, linkers and solvents, and then stir while heating in a microwave. Heat the mixture at 190-210℃ and keep it at that temperature for 28-32h. Then, perform solid-liquid separation, washing and drying at 70-90℃ for 10-14h to obtain MOF materials.

[0040] The rare earth metal element includes any one of yttrium, lanthanum, cerium, praseodymium, or neodymium; the magnetic metal element includes any one of nickel, chromium, iron, or cobalt; the linker includes any one or a combination of at least two of isonicotinic acid, nicotinic acid, 2-aminoisonicotinic acid, methyl isonicotinate, or ethyl isonicotinate; the molar ratio of the salt containing the rare earth metal element to the salt containing the magnetic metal element is (0.8-1.2):1; the molar ratio of the salt containing the rare earth metal element to the linker is 1:(1-1.2).

[0041] The microwave heating power is 360W, the temperature is 50-70℃, and the holding time is 2-5 minutes;

[0042] (2) The MOF material obtained in step (1) is heated to 750-850℃ at a rate of 2-5℃ / min for graphitization treatment and kept at the temperature for 2-4h to obtain the composite microwave absorbing material.

[0043] Secondly, the present invention provides a composite microwave absorbing material based on a MOF structure, wherein the composite microwave absorbing material is prepared by the preparation method described in the first aspect;

[0044] The composite absorbing material has a porous spherical structure;

[0045] The particle size of the composite absorbing material is 5-20μm, for example, it can be 7μm, 9μm, 10μm, 12μm, 14μm, 15μm or 18μm, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0046] It is worth noting that the composite absorbing material has a porous spherical structure. The pores of the particles are located on the surface and run through the entire particle. The pores are basically evenly distributed and present a relatively rough texture. The connectivity of the pores can be observed. The interconnected pore structure will improve the mass transfer and other properties of the material.

[0047] Thirdly, the present invention provides an application of the composite absorbing material described in the second aspect in the field of electromagnetic wave shielding or energy conversion.

[0048] It is worth noting that the composite absorbing material obtained by this invention has a porous spherical structure, which has a higher specific surface area and pore volume, increasing the opportunity for the absorbing material to interact with electromagnetic waves. Furthermore, the composite absorbing material contains magnetic metallic elements and rare earth elements, further enhancing its absorption performance in the X-band.

[0049] In this invention, the composite absorbing material has a maximum reflection loss of -55 to -65 dB at 10 to 12 GHz.

[0050] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] (1) The preparation method provided by the present invention can control the morphology and structure of the material by improving the synthesis strategy and combining the selection of rare earth metals, magnetic metals and linkers, so that it has a higher specific surface area and pore volume, while increasing the interaction opportunities between the absorbing material and electromagnetic waves, improving its absorption performance in the X band, and meeting the requirements of lightweight, wide frequency response and high absorption capacity of the absorbing material.

[0053] (2) The composite absorbing material prepared by the present invention contains magnetic metal elements and rare earth elements. Its porous spherical structure and specific elemental composition give it excellent absorbing performance and can be used in electromagnetic wave shielding or energy conversion and other fields. Attached Figure Description

[0054] Figure 1 The image shows the XRD pattern of the composite absorbing material prepared in Example 1 of this invention.

[0055] Figure 2 This is a SEM image of the composite absorbing material prepared in Example 1 of the present invention;

[0056] Figure 3 This is a reflection loss diagram of the composite absorbing material prepared in Example 1 of the present invention. Detailed Implementation

[0057] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0058] Example 1

[0059] This embodiment provides a composite microwave absorbing material based on a MOF structure, and the preparation method includes the following steps:

[0060] (1) Mix 0.002 mol La(NO3)3·6H2O, 0.002 mol Ni(NO3)2·6H2O, and 0.002 mol isonicotinic acid with a solvent, and then stir while heating in a microwave. Heat the mixture at 200°C and keep it at that temperature for 30 h. Then filter the mixture. Wash the solid obtained with DMF and deionized water at least 3 times. Then dry it at 80°C for 12 h to obtain MOF material.

[0061] The solvent is a mixed solution of DMF (15 mL), anhydrous ethanol (15 mL), and deionized water (15 mL);

[0062] The microwave heating power is 360W, the temperature is 60℃, and the holding time is 2min;

[0063] (2) The MOF material obtained in step (1) is placed in a tube furnace and heated to 800°C at a rate of 3°C / min for graphitization treatment and kept at the temperature for 3 hours to obtain a composite microwave absorbing material.

[0064] The graphitization process is carried out in an argon atmosphere.

[0065] Figure 1 The image shows the XRD pattern of the composite absorbing material prepared in this embodiment. As can be seen from the figure, the composite absorbing material exhibits multiple sets of diffraction peaks, with relatively broad peaks indicating a large crystal size distribution. Furthermore, the weaker peak intensities may indicate a relatively weak crystal structure or some crystal orientation inhomogeneity. Larger pores lead to broader diffraction peaks, while smaller pores may result in relatively sharp peaks.

[0066] Figure 2 The image shows the SEM image of the composite absorbing material prepared in this embodiment. As can be seen from the image, the composite absorbing material consists of porous spherical particles with similar size and size distribution. The pores of the particles are located on the surface and penetrate the entire particle. The pores are basically evenly distributed and exhibit a relatively rough texture. The connectivity of the pores can be preliminarily observed. The interconnected pore structure will affect the mass transfer and other properties of the material.

[0067] Figure 3 The diagram shows the reflection loss of the composite absorbing material prepared in this embodiment. Its maximum reflection loss at 10.8 GHz is -64.52 dB, indicating that in the X-band, the porous spherical particles are small and regular, which can maintain good performance and exhibit high absorption characteristics for electromagnetic waves. This is related to the electromagnetic wave damping properties, loss mechanism or microstructure of the material.

[0068] Example 2

[0069] This embodiment provides a composite microwave absorbing material based on a MOF structure, and the preparation method includes the following steps:

[0070] (1) Mix 0.002 mol Ce(NO3)3·6H2O, 0.002 mol Fe(NO3)3·6H2O, and 0.002 mol methyl isonicotinate with a solvent, and then stir while heating in a microwave. Heat the mixture at 190°C for 32 h and then filter it. Wash the solid obtained with DMF and deionized water at least 3 times, and then dry it at 80°C for 12 h to obtain MOF material.

[0071] The solvent is a mixed solution of DMF (15 mL), anhydrous methanol (15 mL), and deionized water (15 mL);

[0072] The microwave heating power is 360W, the temperature is 70℃, and the holding time is 4min;

[0073] (2) The MOF material obtained in step (1) is placed in a tube furnace and heated to 750°C at a rate of 2°C / min for graphitization treatment and kept at the temperature for 4 hours to obtain a composite microwave absorbing material.

[0074] The graphitization process is carried out in an argon atmosphere.

[0075] Example 3

[0076] This embodiment provides a composite microwave absorbing material based on a MOF structure, and the preparation method includes the following steps:

[0077] (1) Mix 0.018 mol La(NO3)3·6H2O, 0.002 mol Ni(NO3)2·6H2O, and 0.002 mol isonicotinic acid with a solvent, and then stir while heating in a microwave. Heat the mixture at 210 °C for 28 h and keep it warm. Then filter the mixture. Wash the solid obtained with DMF and deionized water at least 3 times. Then dry it at 80 °C for 12 h to obtain MOF material.

[0078] The solvent is a mixed solution of DMF (15 mL), anhydrous methanol (15 mL), and deionized water (15 mL);

[0079] The microwave heating power is 360W, the temperature is 50℃, and the holding time is 5min;

[0080] (2) The MOF material obtained in step (1) is placed in a tube furnace and heated to 850°C at a rate of 5°C / min for graphitization treatment and kept at the temperature for 2 hours to obtain a composite microwave absorbing material.

[0081] The graphitization process is carried out in an argon atmosphere.

[0082] Example 4

[0083] This embodiment provides a composite microwave absorbing material based on MOF structure. Except for adjusting "0.002mol La(NO3)3·6H2O, 0.002mol Ni(NO3)2·6H2O" in step (1) to "0.001mol La(NO3)3·6H2O, 0.003mol Ni(NO3)2·6H2O", all other conditions are the same as in Example 1.

[0084] Example 5

[0085] This embodiment provides a composite microwave absorbing material based on MOF structure. Except for adjusting "0.002mol La(NO3)3·6H2O, 0.002mol Ni(NO3)2·6H2O" in step (1) to "0.003mol La(NO3)3·6H2O, 0.001mol Ni(NO3)2·6H2O", all other conditions are the same as in Example 1.

[0086] Example 6

[0087] This embodiment provides a composite microwave absorbing material based on MOF structure. Except for changing "0.002 mol isonicotinic acid" to "0.002 mol trimesic acid" in step (1), all other conditions are the same as in Example 1.

[0088] Example 7

[0089] This embodiment provides a composite microwave absorbing material based on MOF structure. Except for adjusting "0.002 mol isonicotinic acid" in step (1) to "0.0015 mol isonicotinic acid", all other conditions are the same as in Example 1.

[0090] Example 8

[0091] This embodiment provides a composite microwave absorbing material based on MOF structure. Except for adjusting "0.002 mol isonicotinic acid" in step (1) to "0.003 mol isonicotinic acid", all other conditions are the same as in Example 1.

[0092] Example 9

[0093] This embodiment provides a composite microwave absorbing material based on MOF structure. Except for the microwave heating temperature of 40°C in step (1), all other conditions are the same as in embodiment 1.

[0094] Example 10

[0095] This embodiment provides a composite microwave absorbing material based on MOF structure. Except for the microwave heating temperature of 90°C in step (1), all other conditions are the same as in embodiment 1.

[0096] Example 11

[0097] This embodiment provides a composite microwave absorbing material based on MOF structure. Except for the microwave heating time of 8 minutes in step (2), all other conditions are the same as in embodiment 1.

[0098] Example 12

[0099] This embodiment provides a composite microwave absorbing material based on MOF structure. Except for the graphitization temperature of step (2) being 700℃, all other conditions are the same as in embodiment 1.

[0100] Example 13

[0101] This embodiment provides a composite microwave absorbing material based on MOF structure. Except for the graphitization temperature of step (2) being 900℃, all other conditions are the same as in embodiment 1.

[0102] Comparative Example 1

[0103] This comparative example provides a microwave absorbing material based on a MOF structure. Except for adjusting “0.002mol La(NO3)3·6H2O, 0.002mol Ni(NO3)2·6H2O” in step (1) to “0.004mol La(NO3)3·6H2O”, all other conditions are the same as in Example 1.

[0104] Comparative Example 2

[0105] This comparative example provides a microwave absorbing material based on a MOF structure. Except for adjusting “0.002mol La(NO3)3·6H2O, 0.002mol Ni(NO3)2·6H2O” in step (1) to “0.004mol Ni(NO3)2·6H2O”, all other conditions are the same as in Example 1.

[0106] Comparative Example 3

[0107] This comparative example provides a composite microwave absorbing material based on a MOF structure. Except for step (1) where no pre-reaction was performed (stirring was done while microwave heating), all other conditions are the same as in Example 1.

[0108] The microwave absorbing materials prepared in the above embodiments and comparative examples were tested using a vector network analyzer with the coaxial method. The test results are shown in Table 1.

[0109] Table 1

[0110]

[0111] Among them, the maximum reflection loss in Table 1 is the maximum reflection loss in the 10-12 GHz frequency band; from Table 1, the following points can be derived:

[0112] (1) The composite absorbing material prepared by the preparation method provided in Examples 1-3 of the present invention has a porous spherical structure with uniform particle size distribution. The pores of the particles are located on the surface and penetrate the entire particle. At the same time, it has excellent absorbing performance in the X-band with a maximum reflection loss of -56.12 to -64.52 dB.

[0113] (2) Comparison of Example 1 and Comparative Examples 1-2 shows that when no magnetic metal element or rare earth metal element is added, the synergistic effect of the two cannot be exerted, resulting in a decrease in wave absorption performance.

[0114] The applicant declares that the detailed structural features of the present invention are illustrated through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components selected in the present invention, additions of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing MOF materials, comprising mixing a salt containing rare earth metal elements and magnetic metal elements, a linker, and a solvent, performing a pre-reaction, and then performing a heating reaction to obtain MOF materials, wherein the molar ratio of the rare earth metal elements to the magnetic metal elements is 0.8-1.2:1 (0.8:1, 1.2:1, 0.85:1, 0.9:1, 0.95:1, 1:1, 1.05:1, 1.1:1, or 1.15:1), 1:3, or 3:1; the linker comprises any one or a combination of at least two of isonicotinic acid, nicotinic acid, 2-aminoisonicotinic acid, methyl isonicotinic acid, or ethyl isonicotinic acid, such as isonicotinic acid, nicotinic acid, 2-aminoisonicotinic acid, methyl isonicotinic acid, or ethyl isonicotinic acid, and the pre-reaction comprises microwave heating.

2. The method as described in claim 1, characterized in that, The rare earth metal element includes any one of yttrium, lanthanum, cerium, praseodymium, or neodymium, such as yttrium, lanthanum, cerium, praseodymium, or neodymium; Alternatively, the magnetic metallic element may include any one of nickel, chromium, iron, or cobalt, such as nickel, chromium, iron, or cobalt; Alternatively, the rare earth metal element and / or magnetic metal element may be provided in the form of a salt, which may include any one or a combination of at least two of nitrates, phosphates, sulfates, carbonates or chlorides. Alternatively, the molar ratio of the rare earth metal element to the linker may be 1:1-1.2, 4:3 or 2:3, such as 1:1, 1:1.2, 1:1.02, 1:1.05, 1:1.07, 1:1.09, 1:1.1, 1:1.12, 1:1.12 or 1:1.

15.

3. The method as described in claim 1 or 2, characterized in that, The solvent includes any one or a combination of at least two of N,N-dimethylformamide (DMF), methanol, ethanol, or water, such as containing DMF and water, and also containing methanol or ethanol.

4. The method according to any one of claims 1-3, characterized in that, The microwave heating is used to rapidly improve the solubility and uniformity of the reactants, and / or promote the reaction between metal ions and the linker; Alternatively, the power of the microwave heating is 360W; Alternatively, the microwave heating temperature is 50-70°C, 40°C, or 90°C; Alternatively, the microwave heating holding time is 2-4 minutes or 8 minutes; Alternatively, the stirring can be performed simultaneously with the microwave heating.

5. The method according to any one of claims 1-4, characterized in that, The heating reaction is carried out at a specific temperature and held for a period of time to promote crystal growth and the formation of a porous spherical structure.

6. The method according to any one of claims 1-5, characterized in that, The temperature of the heating reaction is 190-210℃; Alternatively, the holding time for the heating reaction is 28-32 hours.

7. The method according to any one of claims 1-6, characterized in that, The heating reaction is followed by sequential solid-liquid separation, washing, and drying. Alternatively, the drying temperature is 70-90°C; Alternatively, the drying process may be carried out over a period of 10-14 hours.

8. The method according to any one of claims 1-6, characterized in that, The method includes mixing a salt containing rare earth metal elements, a salt containing magnetic metal elements, a linker, and a solvent, then stirring while heating in a microwave, heating and reacting at 190-210℃ for 28-32 hours, followed by solid-liquid separation, washing, and drying at 70-90℃ for 10-14 hours to obtain MOF material. The rare earth metal element includes any one of yttrium, lanthanum, cerium, praseodymium, or neodymium; the magnetic metal element includes any one of nickel, chromium, iron, or cobalt; the linker includes any one or a combination of at least two of isonicotinic acid, nicotinic acid, 2-aminoisonicotinic acid, methyl isonicotinate, or ethyl isonicotinate; the molar ratio of the salt containing the rare earth metal element to the salt containing the magnetic metal element is (0.8-1.2):1; the molar ratio of the salt containing the rare earth metal element to the linker is 1:(1-1.2); the microwave heating power is 360W, the temperature is 50-70℃, and the holding time is 2-4min.

9. A microwave absorbing material prepared by graphitizing any of the MOF materials of the prior claims, wherein the graphitization temperature can be 750-850℃, 700℃ or 900℃; Optionally, the holding time for the graphitization treatment is 2-4 hours; optionally, the heating rate for the graphitization treatment is 2-5°C / min.

10. The use of the material described in any of the prior claims in electromagnetic wave shielding or energy conversion.

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