A rare earth-based organic framework composite material, a preparation method and application thereof

Abstract

This invention discloses a rare-earth-based organic framework composite material, its preparation method, and its applications. The rare-earth-based organic framework composite material includes a core and a shell, with a cavity formed between the core and the shell. The core is an aggregate composed of small particles, including magnetic metals. The shell is a carbonized MOF material, comprising rare-earth elements and magnetic elements. This invention utilizes the carbonization of MOF material to form a shell containing rare-earth elements and magnetic elements, which provides microwave absorption performance. Furthermore, since the core is an aggregate composed of small particles including magnetic metals, it increases the chance of microwave reflection. Additionally, the presence of the cavity increases the reflective interface, further enhancing the material's microwave absorption performance.

Description

Technical Field

[0001] This invention belongs to the field of materials and relates to a rare earth-based organic framework composite material, its preparation method, and its application. Background Technology

[0002] With the rapid development of modern information technology, the application of science and technology in the military field has had an increasingly prominent impact on the outcome of modern warfare. Stealth technology, as one of the key technologies for concealing the whereabouts of weapons and improving strike effectiveness, is constantly being developed and innovated. The X-band is one of the most widely used frequency bands in radar systems. Therefore, military equipment coated with radar-absorbing materials exhibits excellent radar-absorbing performance in the X-band, which can help reduce the radar detection range of targets such as military aircraft, ships, equipment, and drones, improve their stealth and strike capabilities, and gain an advantageous position in military weaponry.

[0003] Traditional X-band absorbing materials, such as ferrites and magnetic metal powders, struggle to simultaneously meet the application requirements of lightweight, wide frequency range, and strong absorption. Metal-organic frameworks (MOFs), on the other hand, are ultraporous materials assembled from metal ions and organic ligands in suitable solvents. Their varied structures and functions, along with extremely high specific surface area and porous structures, provide more absorption opportunities, increasing the multiple reflections and scattering of electromagnetic waves within the material. For example, CN115537180A discloses a two-dimensional conductive MOF absorbing material, its preparation method, and its applications. This patent employs the concept of spatial ordered arrangement and functional unit design to construct two-dimensional conductive MOF absorbing materials with different pore sizes through combinations of different metal coordination ions. The unique two-dimensional layered porous structure, suitable conductivity, polarization loss, conductivity loss, and good impedance matching play a crucial role in the electromagnetic wave attenuation of the two-dimensional conductive MOF.

[0004] Meanwhile, the core-shell structure can protect the internal reflective layer, adapt to the changing environment, provide more reflection opportunities and realize multi-frequency absorption, which can improve the absorption and physical properties of the material. For example, CN116574482A discloses a broadband CoNiFe-MOF composite absorbing material and its preparation method and application. The preparation method is as follows: (1) Preparation of CoNiFe-MOF precursor: Prussian blue (PB) is dissolved in oxalic acid solution, and then cobalt nitrate hexahydrate, nickel nitrate hexahydrate and dimethylimidazole are dissolved in methanol respectively; then the dimethylimidazole solution is poured into the cobalt-nickel composite solution, and Prussian blue solution is poured in, and the reaction is magnetically stirred; the mixed solution after the reaction is centrifuged, washed and dried to obtain CoNiFe-MOF precursor powder; (2) Preparation of broadband CoNiFe-MOF composite absorbing material: the CoNiFe-MOF precursor powder is placed in a muffle furnace in a low oxygen environment for calcination, and after the end, it is cooled to room temperature with the furnace to obtain the broadband CoNiFe-MOF composite absorbing material. The broadband absorbing material prepared using this method has a core-shell structure that facilitates multiple random reflections and scattering of electromagnetic waves within it. At the same time, its abundant defect polarization, dipole polarization, and interface polarization on its surface enhance polarization loss, enabling the absorption of electromagnetic waves to be converted into heat energy.

[0005] However, current common methods for preparing core-shell MOF materials are complex, requiring the separate preparation of the core and outer shell, and the morphology of materials prepared by existing one-step methods is irregular.

[0006] Therefore, developing a new one-step reaction to generate MOF absorbing materials with a core-shell structure and give them good microwave absorption performance is an urgent problem to be solved in the field. Summary of the Invention

[0007] To address the aforementioned problems in the prior art, the present invention aims to provide a rare earth-based organic framework composite material, its preparation method, and its application.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a rare earth-based organic framework composite material, the rare earth-based organic framework composite material comprising a core and a shell, wherein a cavity is formed between the core and the shell, the core being an aggregate composed of small particles, the small particles comprising magnetic metals, and the shell being a carbonized MOF material, the carbonized MOF material comprising rare earth elements and magnetic elements.

[0010] MOF materials are metal-organic frameworks, crystalline materials composed of metal ions or metal clusters and organic ligands. They possess a periodic network structure and exhibit a porous structure. After carbonization, the organic ligands in MOF materials are converted into carbon, while the original periodic network structure is maintained.

[0011] This invention utilizes a self-assembled MOF material to form an outer shell, incorporating rare earth elements and magnetic elements to provide microwave absorption performance. Furthermore, the core is an aggregate of small particles, including magnetic metals, increasing microwave reflection opportunities. The presence of cavities further enhances the reflective interface, further improving the material's microwave absorption performance. The rare earth-based organic framework composite material of this invention achieves a reflection loss as low as 74.39 dB at 10.5 GHz and as low as 44.06 dB at 15.0 GHz.

[0012] In one embodiment, the rare-earth-based organic framework composite material provided by the present invention has a smooth surface, a spherical morphology, and uniform particle size. A spherical microstructure generally implies a uniform structure and composition, which helps ensure uniform distribution of microwave absorption performance throughout the material and improves absorption efficiency.

[0013] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0014] Preferably, the small particles comprise at least two magnetic metals, and the at least two magnetic metals form an alloy;

[0015] Preferably, the magnetic metal includes at least one of nickel, cobalt-neodymium, boron, and samarium.

[0016] Preferably, the rare earth elements in the rare earth oxide include at least one of cerium, lanthanum, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.

[0017] Preferably, the rare earth-based organic framework composite material has a spherical morphology.

[0018] Preferably, the particle size D50 of the rare earth-based organic framework composite material is 1μm to 20μm, for example, it can be 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 12μm, 13μm, 14μm, 15μm, 16μm, 18μm, or 20μm, etc.

[0019] In a second aspect, the present invention provides a method for preparing a rare earth-based organic framework composite material as described in the first aspect, the method comprising the following steps:

[0020] (1) A precursor solution is obtained by mixing a salt containing rare earth elements, a salt containing magnetic metals, and an organic linker with a solvent;

[0021] (2) The precursor solution is subjected to a hydrothermal reaction to obtain the precursor;

[0022] (3) The precursor is carbonized to obtain the rare earth-based organic framework composite material.

[0023] The method of this invention utilizes hydrothermal reaction and carbonization treatment, with an organic linker as a bridging ligand to link the centers of two inorganic metals (rare earth metal and magnetic metal). By utilizing the self-assembly interconnection characteristics of MOF, a type of crystalline porous material with a periodic network structure is formed. A rare earth-based organic framework composite material can be generated in one step, obtaining a complete carbon skeleton (which can be spherical) while retaining the basic properties of rare earth elements and magnetic metal elements.

[0024] The preparation method of the present invention is simple, and the core-shell structure can be obtained in one step, avoiding the cumbersome operation of preparing the core and shell separately in the prior art. Moreover, the core-shell structure prepared by the method of the present invention has a regular morphology and good performance.

[0025] The rare earth-based organic framework composite material prepared by this invention utilizes carbon skeleton, rare earth metal elements and magnetic metal elements to provide microwave absorption performance, while its core-shell structure provides more opportunities for microwave reflection, further increasing reflection loss and absorption bandwidth, giving the product a broader space for exploration and application prospects.

[0026] Preferably, the rare earth element salt and the magnetic metal salt in step (1) are independently selected from any one or a combination of at least two of nitrates, phosphates, sulfates, carbonates or chlorides.

[0027] For example, the salt containing rare earth elements can be Ce(NO3)3·6H2O, and the salt containing magnetic metals can be Ni(NO3)2·6H2O. 3)2 At least one of ·6H2O and Co(NO3)2·6H2O.

[0028] Preferably, in step (1), the molar ratio of the rare earth element in the salt containing rare earth elements to the magnetic metal element in the salt containing magnetic metal is 1:(0.5~2), such as 1:0.5, 1:1, 1:1.5, 1:1.8 or 1:2, etc., but not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] Preferably, the organic linker in step (1) includes at least one of nicotinic acid and its derivatives;

[0030] Preferably, the nicotinic acid derivative includes at least one of isonicotinic acid (4-carboxypyridine), nicotinic acid, 2-aminoisonicotinic acid, methyl isonicotinate, and ethyl isonicotinate.

[0031] It includes at least one of isonicotinic acid (4-carboxypyridine), nicotinic acid, 2-aminoisonicotinic acid, methyl isonicotinate, and ethyl isonicotinate.

[0032] Preferably, the solvent in step (1) includes any one or a combination of at least two of N,N-dimethylformamide, ethanol, or propylene glycol, preferably anhydrous ethanol. The ethanol may be anhydrous ethanol.

[0033] Exemplary examples of the combination include: a combination of N,N-dimethylformamide and anhydrous ethanol, a combination of anhydrous ethanol and propylene glycol, or a combination of N,N-dimethylformamide and propylene glycol. When the solvent is a combination of at least two solvents, the at least two solvents can be mixed in any proportion to form a mixed solvent.

[0034] Preferably, the molar ratio of the rare earth element and the organic linker in step (1) is 1:(1-3), such as 1:1, 1:1.5, 1:1.8, 1:2, 1:2.3, 1:2.6 or 1:3, etc.

[0035] Preferably, the mixing temperature in step (1) is 45°C to 60°C, for example, it can be 45°C, 48°C, 50°C, 52°C, 54°C, 56°C, 58°C, or 60°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable. Mixing within this temperature range can better dissolve the raw materials and form a solution.

[0036] Preferably, the mixing time in step (1) is 10 min to 30 min, for example, it can be 10 min, 12 min, 15 min, 18 min, 20 min, 23 min, 26 min or 30 min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0037] Preferably, the mixing in step (1) is carried out under water bath heating conditions and is accompanied by stirring to fully dissolve the raw materials.

[0038] Preferably, the temperature of the hydrothermal reaction in step (2) is 150℃ to 250℃, for example, it can be 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃ or 250℃, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable. If the temperature is too high, the reaction will produce a reverse reaction, leading to the decomposition of the precipitate; if the temperature is too low, the reaction energy will be insufficient, resulting in an incomplete reaction.

[0039] Preferably, the hydrothermal reaction time in step (2) is 9h to 30h, for example, it can be 9h, 10h, 12h, 15h, 18h, 20h, 24h, 26h, 28h or 30h, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable. If the hydrothermal reaction time is too long, it will first waste time and prolong the preparation cycle, and secondly, it will cause the crystal reaction to be excessive, resulting in changes in morphology. If the hydrothermal reaction time is too short, it will lead to incomplete reaction.

[0040] Preferably, after the hydrothermal reaction in step (2), separation, washing, and drying steps are performed to obtain the hydrothermal product, which is then used for the carbonization treatment in step (3). The present invention does not limit the separation method; filtration can be used. The filtration method can be suction filtration.

[0041] The present invention does not limit the drying method; for example, it can be air drying.

[0042] Preferably, the carbonization temperature in step (3) is 750℃~850℃, for example, it can be 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, 810℃, 820℃, 830℃, 840℃ or 850℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0043] Preferably, the heating rate of the carbonization process in step (3) is 1℃ / min to 5℃ / min, for example, it can be 1℃ / min, 2℃ / min, 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min or 5℃ / min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0044] Preferably, the holding time for carbonization in step (3) is 2.5h to 3.5h, for example, it can be 2.5h, 2.6h, 2.7h, 2.8h, 2.9h, 3.0h, 3.1h, 3.2h, 3.3h, 3.4h, or 3.5h, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable. If the holding time for carbonization is too long, it will lead to a waste of time and energy; if the holding time for carbonization is too short, the precursor cannot be fully carbonized.

[0045] As a preferred embodiment of the preparation method of the rare earth-based organic framework composite material of the present invention, the preparation method includes the following steps:

[0046] (1) After mixing the salt containing rare earth elements, the salt containing magnetic metals and the organic linker with the solvent, the mixture is heated in a water bath at a temperature of 45℃~60℃ for 10min~30min. Stirring is carried out during the water bath heating process to obtain the precursor solution.

[0047] (2) After adding the precursor liquid to the reactor for hydrothermal reaction, the mixture is filtered, washed and dried to obtain the precursor.

[0048] The hydrothermal reaction temperature is 150℃~250℃, and the reaction time is 9h~30h.

[0049] (3) The precursor is carbonized to obtain the rare earth-based organic framework composite material.

[0050] The carbonization treatment temperature is 750℃~850℃, the heating rate is 1℃ / min~5℃ / min, and the holding time is 2.5h~3.5h. Thirdly, this invention provides an application of the rare earth-based organic framework composite material as described in the first aspect, wherein the rare earth-based organic framework composite material is used as a microwave absorbing material.

[0051] Compared with existing technologies, the present invention has the following beneficial effects:

[0052] (1) This invention utilizes MOF materials to autonomously form an outer shell, which contains rare earth elements and magnetic elements, providing microwave absorption performance. Simultaneously, since the core is an aggregate composed of small particles, including magnetic metals, it increases the chance of microwave reflection. Furthermore, the presence of cavities increases the reflective interface, further enhancing the material's microwave absorption performance. The rare earth-based organic framework composite material of this invention can achieve a reflection loss as low as 74.39 dB at 10.5 GHz and as low as 44.06 dB at 15.0 GHz.

[0053] (2) The preparation method of the present invention is simple and the core-shell structure can be obtained in one step, avoiding the cumbersome operation of preparing the core and shell separately in the prior art. Moreover, the core-shell structure prepared by the method of the present invention has a regular morphology and good performance. Attached Figure Description

[0054] Figure 1 The image shows the XRD pattern of the rare earth-based organic framework composite material prepared in Example 1.

[0055] Figure 2 The image shows the reflection loss of the rare earth-based organic framework composite material prepared in Example 1.

[0056] Figure 3 This is a SEM image of the rare earth-based organic framework composite material prepared in Example 1.

[0057] Figure 4 This is a SEM image of the rare earth-based organic framework composite material prepared in Example 2.

[0058] Figure 5 This is a SEM image of the rare earth-based organic framework composite material prepared in Example 3.

[0059] Figure 6 This is a SEM image of the rare earth-based organic framework composite material prepared in Example 4.

[0060] Figure 7 This is a SEM image of the rare earth-based organic framework composite material prepared in Example 5.

[0061] Figure 8 This is a SEM image of the rare earth-based organic framework composite material prepared in Example 6.

[0062] Figure 9 This is a SEM image of the rare earth-based organic framework composite material prepared in Example 7.

[0063] Figure 10 This is a SEM image of the rare earth-based organic framework composite material prepared in Example 8.

[0064] Figure 11 This is a SEM image of the rare earth-based organic framework composite material prepared in Example 9.

[0065] Figure 12 This is a SEM image of the rare earth-based organic framework composite material prepared in Example 10.

[0066] Figure 13 The image shows a SEM image of the rare earth-based organic framework composite material prepared in Comparative Example 1.

[0067] Figure 14 The image shows a SEM image of the rare earth-based organic framework composite material prepared in Comparative Example 2. Detailed Implementation

[0068] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0069] The specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0070] The present invention will be further illustrated below with reference to specific embodiments and comparative examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Operating methods not specifically described in the following embodiments are generally performed under conventional conditions.

[0071] Example 1

[0072] This embodiment provides a rare earth-based organic framework composite material with a spherical morphology and a particle size D50 of 6.9 μm. It includes a core and a shell, with a cavity formed between the core and the shell. The core is an aggregate composed of small particles, which include magnetic metals. The shell is a carbonized MOF material, which includes rare earth elements and magnetic elements.

[0073] Among them, the magnetic metals are Ni and Co, and the rare earth element is Ce.

[0074] The method for preparing rare earth-based organic framework composite materials provided in this embodiment includes the following steps:

[0075] (1) Weigh out Ce(NO3)3·6H2O (0.002mol, 0.8684g), Ni(NO3)2·6H2O (0.001mol, 0.2908g), Co(NO3)2·6H2O (0.001mol, 0.2914g), and isonicotinic acid (0.002mol, 0.2462g) respectively, put them into a beaker, add 30mL of N,N-dimethylformamide (DMF) and 10mL of anhydrous ethanol, and stir thoroughly in a water bath at 60℃ for 20min to obtain a solution;

[0076] (2) Pour the above solution into a reaction vessel and react at a constant temperature of 180℃ for 15h. After the reaction is completed, filter the solution and wash it with anhydrous ethanol multiple times (≥3 times). Place the washed solid in a petri dish and put it into a drying oven at 80℃ for 6h to obtain a rare earth-based spherical MOF with a core-shell structure.

[0077] (3) The above-mentioned rare earth-based spherical MOF with core-shell structure is heated to 800°C at a rate of 3°C / min in a tube furnace and held for 3 hours to obtain the rare earth-based organic framework composite material.

[0078] This embodiment also provides an application of the above-mentioned rare earth-based organic framework composite material as a microwave absorbing material.

[0079] Figure 1 The image shows the XRD pattern of the rare earth-based organic framework composite material prepared in this embodiment. As can be seen from the image, the material has good crystallinity after carbonization. Analysis shows that the outer thin shell is mainly composed of carbon and cerium oxide, and the inner irregular core is a nickel-cobalt alloy.

[0080] Figure 2The diagram shows the reflection loss of the rare earth-based organic framework composite material prepared in this embodiment. The maximum reflection loss is 74.39 dB at 10.5 GHz and 44.06 dB at 15.0 GHz, indicating that it can maintain good performance and exhibit good wave absorption characteristics in the X-band. This is related to the electromagnetic wave damping properties, loss mechanism, or microstructure of the material.

[0081] Figure 3 The image shows the SEM image of the rare earth-based organic framework composite material prepared in this embodiment. As can be seen from the image, the composite material has a regular morphology, small particles, a core-shell structure, and a certain amount of voids between the core and the shell.

[0082] Example 2

[0083] This embodiment provides a rare earth-based organic framework composite material with a spherical morphology and a particle size D50 of 4.52 μm. It includes a core and a shell, with a cavity formed between the core and the shell. The core is an aggregate composed of small particles, which include magnetic metals. The shell is a carbonized MOF material, which includes rare earth elements and magnetic elements.

[0084] Among them, the magnetic metals are Ni and Co, and the rare earth element is Ce.

[0085] The method for preparing rare earth-based organic framework composite materials provided in this embodiment includes the following steps:

[0086] (1) Weigh out Ce(NO3)3·6H2O (0.0013mol, 0.5790g), Ni(NO3)2·6H2O (0.0013mol, 0.3877g), Co(NO3)2·6H2O (0.0013mol, 0.3880g), and isonicotinic acid (0.002mol, 0.2462g), respectively, put them into a beaker, add 30mL of N,N-dimethylformamide (DMF) and 10mL of anhydrous ethanol, and stir thoroughly in a water bath at 60℃ for 20min to obtain a solution;

[0087] (2) Pour the above solution into a reaction vessel and react at a constant temperature of 180℃ for 15h. After the reaction is completed, filter the solution and wash it with anhydrous ethanol multiple times (≥3 times). Place the washed solid in a petri dish and put it into a drying oven at 80℃ for 6h to obtain a rare earth-based spherical MOF with a core-shell structure.

[0088] (3) The above-mentioned rare earth-based spherical MOF with core-shell structure is heated to 800°C at a rate of 3°C / min in a tube furnace and held for 3 hours to obtain the rare earth-based organic framework composite material.

[0089] This embodiment also provides an application of the above-mentioned rare earth-based organic framework composite material as a microwave absorbing material.

[0090] Figure 4 The image shows a SEM image of the rare-earth-based organic framework composite material prepared in Example 2. As can be seen, the composite material exhibits a relatively smooth spherical shape with a clearly defined thin shell. There are certain gaps between the shell and the core. The inner structure is irregular, with small particles clustered together. The core-shell particles have similar sizes and size distributions, providing multiple reflection opportunities on the surfaces of the shell and core. Preliminary assessment suggests that the gaps between the shell and core affect the material's mechanical and wave-absorbing properties.

[0091] Example 3

[0092] This embodiment provides a rare earth-based organic framework composite material with a spherical morphology and a particle size D50 of 8.27 μm. It includes a core and a shell, with a cavity formed between the core and the shell. The core is an aggregate composed of small particles, which include magnetic metals. The shell is a carbonized MOF material, which includes rare earth elements and magnetic elements.

[0093] Among them, the magnetic metals are Ni and Co, and the rare earth element is Ce.

[0094] The preparation method of the rare earth-based organic framework composite material provided in this embodiment differs from that in Example 1 in that 30 mL of DMF and 10 mL of anhydrous ethanol are replaced with 40 mL of anhydrous ethanol.

[0095] Figure 5 The image shows a SEM image of the rare earth-based organic framework composite material prepared in this embodiment. As can be seen from the image, the rare earth-based organic framework composite material prepared in this embodiment has a similar morphology to the composite material in Example 1, but the spherical shape is smoother and fuller. This indicates that the type of solvent has a significant impact on the morphology of the composite material. Anhydrous ethanol, compared to a mixture of DMF and anhydrous ethanol, is more conducive to forming a smooth and full morphology.

[0096] This embodiment also provides an application of the above-mentioned rare earth-based organic framework composite material as a microwave absorbing material.

[0097] Example 4

[0098] This embodiment provides a rare earth-based organic framework composite material with a spherical morphology and a particle size D50 of 5.51 μm. It includes a core and a shell, with a cavity formed between the core and the shell. The core is an aggregate composed of small particles, which include magnetic metals. The shell is a carbonized MOF material, which includes rare earth elements and magnetic elements.

[0099] Among them, the magnetic metals are Ni and Co, and the rare earth element is Ce.

[0100] The difference between the preparation method of the rare earth-based organic framework composite material provided in this embodiment and that in Example 2 is that 30 mL DMF and 10 mL anhydrous ethanol are replaced with 20 mL DMF and 20 mL anhydrous ethanol.

[0101] Figure 6 This is a SEM image of the rare earth-based organic framework composite material prepared in this embodiment. The rare earth-based organic framework composite material prepared in this embodiment has a similar morphology to the composite material in Example 1, but its shell is thicker and the aggregation of the core contents is more obvious. It can be seen that when the solvent is a mixture of DMF and anhydrous ethanol, the volume ratio of DMF to anhydrous ethanol will affect the morphology of the composite material.

[0102] This embodiment also provides an application of the above-mentioned rare earth-based organic framework composite material as a microwave absorbing material.

[0103] Example 5

[0104] A rare earth-based organic framework composite material, its preparation method, and its uses are disclosed. The preparation method differs from that in Example 1 only in that the amount of metal salt added is changed to Ce(NO3)3·6H2O (0.0024mol, 1.0421g), Ni(NO3)2·6H2O (0.0012mol, 0.3489g), Co(NO3)2·6H2O (0.0012mol, 0.3492g), and isonicotinic acid (0.002mol, 0.2462g).

[0105] Figure 7 This is a SEM image of the rare-earth-based organic framework composite material prepared in this embodiment. The rare-earth-based organic framework composite material prepared in this embodiment has a similar morphology to the composite material in Example 1. However, due to the mismatch between the rare-earth ion ratio and the linker, the structural reaction is incomplete, resulting in pores in its shell. This leads to uneven dispersion in the system when used as a microwave-absorbing material to prepare a stealth coating, thereby reducing the performance of the stealth coating. Example 6

[0106] This embodiment provides a rare earth-based organic framework composite material with a spherical morphology and a particle size D50 of 8.2 μm. It includes a core and a shell, with a cavity formed between the core and the shell. The core is an aggregate composed of small particles, which include magnetic metals. The shell is a carbonized MOF material, which includes rare earth elements and magnetic elements.

[0107] Among them, the magnetic metals are Ni and Co, and the rare earth element is Ce.

[0108] The preparation method of rare earth-based organic framework composite material provided in this embodiment includes the following steps: (1) Weigh Ce(NO3)3·6H2O (0.0024mol, 1.0421g), Ni(NO3)2·6H2O (0.0008mol, 0.2326g), Co(NO3)2·6H2O (0.0008mol, 0.2328g), and isonicotinic acid (0.002mol, 0.2462g) respectively, put them into a beaker, add 10mL of propylene glycol and 30mL of anhydrous ethanol, and stir thoroughly in a water bath at 50℃ for 30min to obtain a solution;

[0109] (2) Pour the above solution into a reaction vessel and react at a constant temperature of 210℃ for 10h. After the reaction is completed, filter the solution and wash it with anhydrous ethanol multiple times (≥3 times). Place the washed solid in a petri dish and put it into a drying oven at 85℃ for 4h to obtain a rare earth-based spherical MOF with a core-shell structure.

[0110] (3) The above-mentioned rare earth-based spherical MOF with core-shell structure is heated to 850°C at a rate of 5°C / min in a tube furnace and held for 2.5h to obtain the rare earth-based organic framework composite material.

[0111] This embodiment also provides an application of the above-mentioned rare earth-based organic framework composite material as a microwave absorbing material.

[0112] Figure 8 The image shows a SEM image of the rare earth-based organic framework composite material prepared in this embodiment. As can be seen from the image, the rare earth-based organic framework composite material prepared in this embodiment has a similar morphology to the composite material in Example 1. The composite material is generally a smooth sphere with a clear thin shell layer on the outside and a certain gap between the shell layer and the core.

[0113] Example 7

[0114] A rare earth-based organic framework composite material, its preparation method and uses, the preparation method differs from that of Example 1 only in that the constant temperature in step (2) in the reactor is 140°C.

[0115] Figure 9 This is a SEM image of the rare earth-based organic framework composite material prepared in this embodiment. The rare earth-based organic framework composite material prepared in this embodiment has a similar morphology to the composite material in Example 1, but its shell surface is rough. Due to the lower reaction temperature, the reaction is incomplete, the core is not fully grown, and there are more unreacted linker impurities.

[0116] Example 8

[0117] A rare earth-based organic framework composite material, its preparation method and uses, the preparation method differs from that of Example 1 only in that the constant temperature in step (2) in the reactor is 260°C.

[0118] Figure 10 This is a SEM image of the rare-earth-based organic framework composite material prepared in this embodiment. Due to excessively high temperature, the system reacted violently, the products decomposed, and the structure collapsed.

[0119] Example 9

[0120] A rare earth-based organic framework composite material, its preparation method and uses, the preparation method differs from that of Example 1 only in that the constant temperature time in step (2) in the reactor is 8h.

[0121] Figure 11 This is a SEM image of the rare earth-based organic framework composite material prepared in this embodiment. Due to the short reaction time, the reaction was incomplete, and most of the products existed in the form of irregular spherical aggregates.

[0122] Example 10

[0123] A rare earth-based organic framework composite material, its preparation method and uses, the preparation method differs from that of Example 1 only in that the constant temperature time in step (2) in the reactor is 31h.

[0124] Figure 12 This is a SEM image of the rare earth-based organic framework composite material prepared in this embodiment. A small portion of the rare earth-based organic framework composite material prepared in this embodiment still has a similar morphology to the composite material in Example 1. Due to excessively long reaction time, the product decomposes again, and wrinkles appear on the smooth surface.

[0125] Comparative Example 1

[0126] This comparative example provides a method for preparing a rare earth-based MOF, which differs from Example 1 only in the addition of deionized water (20 mL) and anhydrous ethanol (20 mL).

[0127] Comparative Example 2

[0128] This comparative example provides a method for preparing a rare earth-based MOF, which differs from Example 4 only in that the metal nitrates added are Ce(NO3)3·6H2O (0.0027mol, 1.1579g), Ni(NO3)2·6H2O (0.00067mol, 0.1939g), and Co(NO3)2·6H2O (0.00067mol, 0.1940g).

[0129] Figure 13 and Figure 14The images show SEM images of the rare earth-based organic framework composites prepared in Comparative Example 1 and Comparative Example 2, respectively. As can be seen from the images, the products have irregular morphology, rough surfaces, and uneven sizes, and do not possess a core-shell structure.

[0130] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0131] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A rare earth-based organic framework composite material, characterized in that, The rare earth-based organic framework composite material includes a core and a shell, with a cavity formed between the core and the shell. The core is an aggregate composed of small particles, including magnetic metals. The shell is a carbonized MOF material, which includes rare earth elements and magnetic elements.

2. The rare earth-based organic framework composite material according to claim 1, characterized in that, The small particles comprise at least two magnetic metals, which form an alloy.

3. The rare earth-based organic framework composite of claim 1, wherein, The magnetic metal includes at least one of nickel, cobalt, neodymium, boron, and samarium.

4. The rare earth-based organic framework composite of claim 1, wherein, The rare earth elements include at least one of cerium, lanthanum, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.

5. The rare earth-based organic framework composite of claim 1, wherein, The rare earth-based organic framework composite material has a spherical morphology.

6. The rare earth-based organic framework composite of claim 1, wherein, The particle size D50 of the rare earth-based organic framework composite material is 1 μm to 20 μm.

7. A method of preparing a rare earth based organic framework composite material as claimed in any one of claims 1 to 6, characterised in that, The preparation method includes the following steps: (1) A precursor solution is obtained by mixing a salt containing rare earth elements, a salt containing magnetic metals, and an organic linker with a solvent; (2) The precursor solution is subjected to a hydrothermal reaction to obtain the precursor; (3) The precursor is carbonized to obtain the rare earth-based organic framework composite material.

8. The method for preparing the rare earth-based organic framework composite material according to claim 7, characterized in that, The rare earth element salt and the magnetic metal salt mentioned in step (1) are independently selected from any one or at least a combination of two of the following: nitrates, phosphates, sulfates, carbonates or chlorides.

9. The method for preparing rare earth-based organic framework composite materials according to claim 7, characterized in that, In step (1), the molar ratio of rare earth elements in the salt containing rare earth elements to magnetic metal elements in the salt containing magnetic metals is 1:(0.5~2).

10. The method for preparing the rare earth-based organic framework composite material according to claim 7, characterized in that, The organic linker in step (1) includes at least one of nicotinic acid and its derivatives; The nicotinic acid derivatives include at least one of isonicotinic acid (4-carboxypyridine), 2-aminoisonicotinic acid, methyl isonicotinic acid, and ethyl isonicotinic acid.

11. The method for preparing rare earth-based organic framework composite materials according to claim 7, characterized in that, The solvent in step (1) includes any one or a combination of at least two of N,N-dimethylformamide, ethanol or propylene glycol.

12. The method for preparing the rare earth-based organic framework composite material according to claim 11, characterized in that, The solvent used in step (1) is anhydrous ethanol.

13. The method for preparing the rare earth-based organic framework composite material according to claim 7, characterized in that, The molar ratio of the rare earth element and the organic linker in step (1) is 1:(1~3).

14. The method for preparing the rare earth-based organic framework composite material according to claim 7, characterized in that, The mixing temperature in step (1) is 45℃~60℃.

15. The method for preparing rare earth-based organic framework composite materials according to claim 7, characterized in that, The temperature of the hydrothermal reaction in step (2) is 150℃~250℃.

16. The method for preparing the rare earth-based organic framework composite material according to claim 7, characterized in that, The hydrothermal reaction time in step (2) is 9h~30h.

17. The method for preparing the rare earth-based organic framework composite material according to claim 7, characterized in that, The carbonization temperature in step (3) is 750℃~850℃.

18. The method for preparing the rare earth-based organic framework composite material according to claim 7, characterized in that, The heating rate of the carbonization process in step (3) is 1℃ / min to 5℃ / min.

19. The method for preparing rare earth-based organic framework composite materials according to claim 7, characterized in that, The heat preservation time for carbonization treatment in step (3) is 2.5h~3.5h.

20. The method for preparing the rare earth-based organic framework composite material according to claim 7, characterized in that, The preparation method includes the following steps: (1) After mixing the salt containing rare earth elements, the salt containing magnetic metals and the organic linker with the solvent, the mixture is heated in a water bath at a temperature of 45℃~60℃ for 10min~30min. Stirring is carried out during the water bath heating process to obtain the precursor solution. (2) After the precursor liquid is added to the reactor for hydrothermal reaction, it is filtered, washed and dried to obtain the precursor; The hydrothermal reaction temperature is 150℃~250℃, and the reaction time is 9h~30h. (3) The precursor is subjected to carbonization treatment to obtain the rare earth-based organic framework composite material; The carbonization treatment temperature is 750℃~850℃, the heating rate is 1℃ / min~5℃ / min, and the holding time is 2.5h~3.5h.

21. Use of a rare earth based organic framework composite material as claimed in any one of claims 1 to 6, characterized in that, The rare earth-based organic framework composite material is used as a microwave absorbing material.

Images