Preparation methods and applications of MOF-derived A-site doped ABO3 perovskite materials

Abstract

This invention relates to a method for preparing and applying MOF-derived A-site-doped ABO3-type perovskite materials. The purpose of this invention is to address the problem that existing methods for preparing A-site-doped ABO3-type perovskite materials are limited in scope and result in poor absorption performance when used as microwave absorbing materials. Unlike the traditional sol-gel method followed by high-temperature calcination, this invention controls the hydrolysis process of the MOF matrix, followed by high-temperature calcination to obtain the perovskite material, which is then applied as a microwave absorbing material in the field of electromagnetic wave absorption. The MOF-derived A-site-doped ABO3-type perovskite material prepared by this invention achieves a reflection loss of -62.6 dB at 11 GHz when used as a microwave absorbing material, with a material thickness of only 2.08 mm. Furthermore, when the material thickness is 5 mm, its absorption band can be as low as 4 GHz, achieving a reflection loss of -34 dB.

Description

Technical Field

[0001] This invention relates to the preparation method and application of ABO3 type perovskite materials. Background Technology

[0002] ABO3-type perovskites refer to a class of ceramic oxides, typically exhibiting single-perovskite, double-perovskite, and layered perovskite structures. The general chemical formula for simple oxide perovskites is ABO3, where A is usually a large-radius rare-earth or alkaline-earth metal element, such as Ca, Sr, or Ba; B is a small-radius transition metal element, such as Ti, Mn, Fe, or Co, which are elements with variable valence states; and O is oxygen. Common ABO3-type perovskites include LaFnO3 and BiFeO3.

[0003] Typically, most metallic elements can become A or B ions in ABO3-type perovskites, and both the A and B sites can be partially substituted by other metal ions of similar radius while maintaining the basic crystal structure. Furthermore, their physical and chemical properties can vary greatly depending on the constituent elements A and B. In recent years, perovskite oxides have not only been an important research subject in the ceramics industry but have also been developed as novel smart materials. To date, extensive research has been conducted on their ferromagnetic, superconducting, and catalytic properties.

[0004] However, current A-site doped ABO3 perovskite materials are typically obtained through sol-gel methods and high-temperature calcination, resulting in limited preparation methods. When used as microwave absorbing materials, their absorption performance is poor, and the high filler ratio (>70 wt%) fails to meet the design requirements for high-performance, lightweight microwave absorbing materials. For example, Reference 1 synthesized A-site Sr-doped LaFeO3 materials using the sol-gel method. When the filler ratio of the absorbing material in the absorbing agent was 80 wt%, the optimal reflection loss was only -39.3 dB, with a thickness of 2.2 mm, which does not meet the design requirements for high-performance, lightweight microwave absorbing materials. Therefore, it is necessary to develop a method for preparing A-site doped ABO3 perovskite composite materials that achieves low filler ratios and high absorption performance.

[0005] Document 1: HUANG L, CHENG L, PAN S, et al. Effects of Sr doping on the structure, magnetic properties and microwave absorption properties of LaFeO3 nanoparticles[J]. Ceramics International, 2020, 46(17): 27352-61. Summary of the Invention

[0006] The purpose of this invention is to address the problems of existing methods for preparing A-site doped ABO3 perovskite materials, which suffer from limited preparation methods, high filler ratios, and poor absorption performance when used as microwave absorbing materials. This invention provides a novel preparation method for MOF-derived A-site doped ABO3 perovskite materials and applies it to the field of electromagnetic wave absorption.

[0007] The preparation method of MOF-derived A-site doped ABO3 perovskite material is carried out according to the following steps:

[0008] I. Preparation of MOF matrix:

[0009] ① Dissolve the cobalt salt in DMF to obtain a cobalt salt solution;

[0010] ② Dissolve pyromellitic acid in DMF to obtain a pyromellitic acid solution;

[0011] ③ Mix the cobalt salt solution and the trimesic 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;

[0012] II. Preparation of MOF-based composite materials coated with hydroxide precipitates:

[0013] ① Dissolve the nitrates of the A-site elements of two types of ABO3 perovskites in deionized water to obtain mixed solution I;

[0014] The nitrates of the A-site elements in the two types of ABO3 perovskites mentioned in step 2① are two of the following: La(NO3)3·6H2O, Sm(NO3)3·6H2O, Cr(NO3)3·9H2O, and Bi(NO3)3·5H2O.

[0015] ② Disperse the MOF matrix in deionized water to obtain mixed solution II;

[0016] ③ Mix solution I and solution II thoroughly to obtain a mixed solution; let stand for a period of time and collect the precipitate; wash the precipitate with ethanol and then vacuum dry to obtain the MOF-based composite material coated with hydroxide precipitate;

[0017] III. High-temperature calcination:

[0018] MOF-based composite materials coated with hydroxide precipitate were heated to 600℃~1000℃ in an argon atmosphere and then held at 600℃~1000℃ for a period of time to obtain MOF-derived A-site doped ABO3 type perovskite materials.

[0019] MOF-derived A-site doped ABO3 perovskite materials are used as microwave absorbing materials.

[0020] Advantages of this invention:

[0021] I. The purpose of this invention is to utilize the spontaneous hydrolysis process of Co-MOF in water, through a co-precipitation process, to allow the two A-site metal elements doped and the B-site elements in the matrix to simultaneously form hydroxide precipitates and adhere to the outside of the matrix. Through subsequent high-temperature calcination, the A-site doped perovskite phase is spontaneously assembled in the MOF material. The synthesized material exists in a fine powder state and has the characteristics of controllable morphology, simple synthesis, and pollution-free synthesis process.

[0022] II. The microstructure of the MOF-derived A-site doped ABO3 perovskite material prepared by this invention is a spherical structure with an average diameter of 1 μm.

[0023] Third, compared with existing methods for A-site doping of ABO3 type perovskites, the advantages of this invention are that the synthesized material has a monomer structure, uniform grain size, stable material structure, and the size can be controlled by the hydrothermal process, and the synthesis method is simple.

[0024] IV. When the MOF-derived A-site doped ABO3 perovskite material prepared in this invention is used as an absorbing material, it achieves a reflection loss of -62.6 dB at 11 GHz, with a material thickness of only 2.08 mm. Furthermore, when the material thickness is 5 mm, its absorption band can be as low as 4 GHz, achieving a reflection loss of -34 dB.

[0025] This invention provides a method for preparing and applying MOF-derived A-site doped ABO3-type perovskite materials. Attached Figure Description

[0026] Figure 1 MOF-derived A-site doped ABO3 type perovskite material (Sm) prepared in Example 1 x La 1- X-ray diffraction pattern of xCoO3;

[0027] Figure 2 MOF-derived A-site doped ABO3 type perovskite material (Sm) prepared in Example 1 x La 1- SEM image of xCoO3;

[0028] Figure 3 MOF-derived A-site doped ABO3 type perovskite material (Sm) prepared in Example 1 x La 1- Image of the real and imaginary parts of the complex permittivity of xCoO3 at frequencies from 2 to 18 GHz;

[0029] Figure 4MOF-derived A-site doped ABO3 type perovskite material (Sm) prepared in Example 1 x La 1- Images of the real and imaginary parts of the complex permeability of xCoO3 at frequencies from 2 to 18 GHz;

[0030] Figure 5 MOF-derived A-site doped ABO3 type perovskite material (Sm) prepared in Example 1 x La 1- The reflection loss curves of xCoO3 are shown in the figure, with curve thicknesses of 1.7 mm, 1.9 mm, 2.08 mm, 2.3 mm, 3 mm, 4 mm, and 5 mm, respectively. Detailed Implementation

[0031] Specific Implementation Method 1: The preparation method of MOF-derived A-site doped ABO3 type perovskite material in this implementation method is carried out according to the following steps:

[0032] I. Preparation of MOF matrix:

[0033] ① Dissolve the cobalt salt in DMF to obtain a cobalt salt solution;

[0034] ② Dissolve pyromellitic acid in DMF to obtain a pyromellitic acid solution;

[0035] ③ Mix the cobalt salt solution and the trimesic 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;

[0036] II. Preparation of MOF-based composite materials coated with hydroxide precipitates:

[0037] ① Dissolve the nitrates of the A-site elements of two types of ABO3 perovskites in deionized water to obtain mixed solution I;

[0038] The nitrates of the A-site elements in the two types of ABO3 perovskites mentioned in step 2① are two of the following: La(NO3)3·6H2O, Sm(NO3)3·6H2O, Cr(NO3)3·9H2O, and Bi(NO3)3·5H2O.

[0039] ② Disperse the MOF matrix in deionized water to obtain mixed solution II;

[0040] ③ Mix solution I and solution II thoroughly to obtain a mixed solution; let stand for a period of time and collect the precipitate; wash the precipitate with ethanol and then vacuum dry to obtain the MOF-based composite material coated with hydroxide precipitate;

[0041] III. High-temperature calcination:

[0042] MOF-based composite materials coated with hydroxide precipitate were heated to 600℃~1000℃ in an argon atmosphere and then held at 600℃~1000℃ for a period of time to obtain MOF-derived A-site doped ABO3 type perovskite materials.

[0043] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that: the cobalt salt mentioned in step one ① is one or a mixture of several of cobalt nitrate hydrate, cobalt chloride hydrate, and cobalt sulfate hydrate; the molar ratio of the cobalt salt to the volume of DMF in step one ① is (2mmol~6mmol):(20mL~60mL). The other steps are the same as in Specific Implementation Method One.

[0044] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that: in step 1, ②, pyromellitic acid is dissolved in DMF under stirring or ultrasonic conditions to obtain a pyromellitic acid solution; the molar ratio of pyromellitic acid to DMF in step 1, ② is (1 mmol to 3 mol): (20 mL to 60 mL). Other steps are the same as in Specific Implementation Method 1 or 2.

[0045] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that: the volume ratio of the cobalt salt solution to the trimesic acid solution in step one, step three is (20 mL to 60 mL):(20 mL to 60 mL); the stirring time in step one, step three is 10 min to 20 min. Other steps are the same as in Specific Implementation Methods One to Three.

[0046] 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 150℃~180℃, and the hydrothermal reaction time is 10h~16h; in step one ③, the reaction product is centrifuged and washed 3 to 5 times with anhydrous ethanol, 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.

[0047] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that: the molar ratio between the nitrates of the A-site elements of the two ABO3-type perovskites described in step two① is 1:(1-9); the molar ratio of the amount of nitrates of the A-site elements of the two ABO3-type perovskites to the volume of deionized water in step two① is 1 mmol:(20 mL-60 mL). The other steps are the same as in Specific Implementation Methods One to Five.

[0048] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that: in step two ②, the mass ratio of the MOF matrix to the volume of deionized water is (300mg~600mg):(30mL~60mL); in step two ③, the mass ratio of the MOF matrix to the molar ratio of the nitrates of the A-site elements of the two ABO3-type perovskites in the mixed solution is (300mg~600mg):(1mmol~3mmol). The other steps are the same as in Specific Implementation Methods One to Six.

[0049] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that: the standing time in step two to three is 30 to 240 minutes; in step two to seven, the precipitate is washed with ethanol 3 to 5 times, and then vacuum dried at 60°C to 70°C for 10 to 12 hours to obtain the MOF-based composite material coated with hydroxide precipitate. Other steps are the same as in Specific Implementation Methods One to Seven.

[0050] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that: the heating rate in step three is 2℃ / min to 10℃ / min; the holding time in step three is 120min to 360min. Other steps are the same as in Specific Implementation Methods One to Eight.

[0051] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that: MOF-derived A-site doped ABO3 type perovskite material is used as the microwave absorbing material. The other steps are the same as in Specific Implementation Methods One to Nine.

[0052] The beneficial effects of the present invention are verified using the following embodiments:

[0053] Example 1: This example aims to expand the selection of existing methods for preparing ABO3-type perovskites and obtain highly efficient electromagnetic wave absorbing materials. This invention is based on the metallic Co in Co-MOFs. 2+ Ions, utilizing the spontaneous hydrolysis process of Co-MOF combined with the addition of A-site elements, yielded composite materials with various hydroxide precipitates as coatings. A-site-doped ABO3 perovskite materials were prepared by high-temperature calcination, increasing the synthesis of ABO3-type perovskite materials and allowing for selective A-site doping. The preparation method of the MOF-derived A-site-doped ABO3-type perovskite material in this embodiment is specifically carried out according to the following steps:

[0054] I. Preparation of MOF matrix:

[0055] ① Dissolve 2 mmol Co(NO3)2·6H2O in 40 mL DMF to obtain a cobalt salt solution;

[0056] ② Dissolve 1 mmol of pyromellitic acid in 20 mL of DMF under stirring and sonication conditions to obtain a pyromellitic acid solution;

[0057] ③ Mix the cobalt salt solution and the trimesic acid solution and stir for 10 min to obtain a mixed solution; subject the mixed solution to a hydrothermal reaction at 160 °C for 10 h to obtain the reaction product; wash the reaction product three times by centrifugation with anhydrous ethanol, and then vacuum dry at 60 °C for 12 h to obtain the MOF matrix;

[0058] II. Preparation of MOF-based composite materials coated with hydroxide precipitates:

[0059] ① Dissolve 1 mmol La(NO3)3·6H2O and 1 mmol Sm(NO3)3·6H2O in 60 mL of deionized water to obtain mixed solution I;

[0060] ② Disperse 600 mg of MOF matrix into 60 mL of deionized water to obtain mixed solution II;

[0061] ③ Mix solution I and solution II evenly to obtain a mixed solution; let stand for 60 min and collect the precipitate; wash the precipitate three times with ethanol, and then vacuum dry at 60℃ for 12 h to obtain the MOF-based composite material with hydroxide precipitate on the outside.

[0062] III. High-temperature calcination:

[0063] MOF-based composites coated with hydroxide precipitate were heated to 700℃ at a heating rate of 5℃ / min under argon atmosphere and held at 700℃ for 240 min to obtain MOF-derived A-site doped ABO3 type perovskite material (Sm x La 1- xCoO3);

[0064] IV. Preparation of microwave absorbing agent:

[0065] The MOF-derived A-site-doped ABO3-type perovskite material (Sm) prepared in step three was used. x La 1- xCoO3) and paraffin are mixed evenly at a mass ratio of 4:6. Then cyclohexane is added and mixed evenly at 70°C. After drying, the mixture is 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.

[0066] The Sm mentioned in step four x La 1- The mass-to-volume ratio of xCoO3, paraffin, and cyclohexane is 400 mg: 600 mg: 1 mL.

[0067] Figure 1MOF-derived A-site doped ABO3 type perovskite material (Sm) prepared in Example 1 x La 1- X-ray diffraction pattern of xCoO3;

[0068] Depend on Figure 1 It can be seen that after calcination at 700℃, the diffraction peaks of the obtained sample show a leftward shift of SmCoO3. This is because the added Sm... 3+ Slightly smaller than La 3+ The ionic radii and leftward shift of the peak positions demonstrate that the MOF material coated with hydroxide precipitate successfully derives Sm after high-temperature calcination. x La 1- The xCoO3 phase, along with the coexisting Co3O4 phase, provides the material with a certain degree of magnetism.

[0069] Figure 2 MOF-derived A-site doped ABO3 type perovskite material (Sm) prepared in Example 1 x La 1- SEM image of xCoO3;

[0070] Depend on Figure 2 It can be seen that the A-site doped Sm prepared by this invention x La 1- The microstructure of the xCoO3 multiphase composite material is spherical with an average diameter of 1 μm and a large number of pores on the surface.

[0071] The electromagnetic parameters of the microwave absorber prepared in Example 1 were tested using a vector network analyzer, see [link to example]. Figures 3-4 As shown;

[0072] Figure 3 MOF-derived A-site doped ABO3 type perovskite material (Sm) prepared in Example 1 x La 1- Image of the real and imaginary parts of the complex permittivity of xCoO3 at frequencies from 2 to 18 GHz;

[0073] Depend on Figure 3 It can be seen that the MOF-derived A-site doped ABO3 type perovskite material (Sm) prepared in Example 1 x La 1- The real and imaginary parts of the complex permittivity of xCoO3 decrease slowly with increasing frequency in the 2-18 GHz band, with the real part decreasing from 12.1 to 8.5 and the imaginary part decreasing from 4.07 to 1.27.

[0074] Figure 4 MOF-derived A-site doped ABO3 type perovskite material (Sm) prepared in Example 1 x La 1-Images of the real and imaginary parts of the complex permeability of xCoO3 at frequencies from 2 to 18 GHz;

[0075] Depend on Figure 4 It can be seen that the MOF-derived A-site doped ABO3 type perovskite material (Sm) prepared in Example 1 x La 1- xCoO3) exhibits a certain degree of magnetism, mainly due to the presence of the magnetic phase Co3O4; Sm x La 1- The real and imaginary parts of the complex permeability of xCoO3 decrease slowly with increasing frequency in the 2-18 GHz band, with the real part decreasing from 1.43 to 0.97 and the imaginary part decreasing from 0.17 to 0.14.

[0076] Compared to traditional A-site doped perovskite absorbing materials, this invention utilizes the metal nodes provided by the MOF material itself to combine with the desired perovskite A-site elements. High-temperature calcination spontaneously generates a new phase within the material. Depending on the requirements, suitable perovskite materials can be selected to control the performance defects of the MOF matrix material, while also balancing impedance matching to achieve the optimal absorption performance.

[0077] With a fixed absorber thickness, the absorption performance of the absorbing material at different frequencies was tested. Figure 5 As shown;

[0078] Figure 5 MOF-derived A-site doped ABO3 type perovskite material (Sm) prepared in Example 1 x La 1- The reflection loss curves of xCoO3 are shown in the figure, with curve thicknesses of 1.7 mm, 1.9 mm, 2.08 mm, 2.3 mm, 3 mm, 4 mm, and 5 mm, respectively.

[0079] Depend on Figure 5 It can be seen that the MOF-derived A-site doped ABO3 perovskite material prepared in Example 1 can achieve a reflection loss of -62.8 dB at 11 GHz, with a material thickness of only 2.08 mm. When the material thickness is 5 mm, its absorption band can be as low as 4 GHz, and it can have a reflection loss of -34 dB.

[0080] Compared with the traditional synthesis method of A-site doped ABO3 type perovskite materials, this invention uses the metal nodes provided by the MOF material itself to combine with the required perovskite A-site elements, and uses high-temperature calcination to spontaneously generate new phases inside. According to the requirements, appropriate A-site elements can be selected, and the obtained microwave absorbing material is superior to most existing A-site doped perovskite microwave absorbing materials.

[0081] The preparation process of this invention is simple, the synthesis process is safe and pollution-free, and the filling ratio of microwave absorbing material in the microwave absorbing agent is only 40 wt% compared with traditional A-site doped perovskite materials (>70 wt%). The morphology of the prepared material is controllable and the performance is better, providing a reference for the derivation of various A-site doped perovskite phases of MOFs.

Claims

1. A method for preparing MOF-derived A-site doped ABO3 type perovskite materials, characterized in that... The preparation method is specifically carried out according to the following steps: I. Preparation of MOF matrix: ① Dissolve the cobalt salt in DMF to obtain a cobalt salt solution; ② Dissolve pyromellitic acid in DMF to obtain a pyromellitic acid solution; ③ Mix the cobalt salt solution and the trimesic 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 coated with hydroxide precipitates: ① Dissolve the nitrates of the A-site elements of two types of ABO3 perovskites in deionized water to obtain mixed solution I; The nitrates of the A-site elements in the two types of ABO3 perovskites mentioned in step 2① are two of the following: La(NO3)3·6H2O, Sm(NO3)3·6H2O, Cr(NO3)3·9H2O, and Bi(NO3)3·5H2O. The molar ratio between the nitrates of the A-site elements in the two types of ABO3 perovskites mentioned in step 2① is 1:(1~9); ② Disperse the MOF matrix in deionized water to obtain mixed solution II; ③ Mix mixed solution I and mixed solution II thoroughly to obtain a mixed solution; let it stand for a period of time and collect the precipitate; The precipitate was washed with ethanol and then vacuum dried to obtain a MOF-based composite material coated with hydroxide precipitate. In step 2③, the mass ratio of the MOF matrix to the nitrates of the A-site elements of the two ABO3 perovskites in the mixed solution is (300mg~600mg):(1mmol~3mmol); III. High-temperature calcination: MOF-based composite materials coated with hydroxide precipitate were heated to 600℃~1000℃ in an argon atmosphere and then held at 600℃~1000℃ for a period of time to obtain MOF-derived A-site doped ABO3 type perovskite material. The heat preservation time mentioned in step three is 120 min to 360 min.

2. The method for preparing MOF-derived A-site doped ABO3 perovskite material according to claim 1, characterized in that... The cobalt salt mentioned in step 1① is one or a mixture of several of cobalt nitrate hydrate, cobalt chloride hydrate and cobalt sulfate hydrate; the molar ratio of the cobalt salt to the volume of DMF in step 1① is (2mmol~6mmol):(20mL~60mL).

3. The method for preparing MOF-derived A-site doped ABO3-type perovskite material according to claim 1, characterized in that... In step 1 and 2, pyromellitic acid is dissolved in DMF under stirring or ultrasonic conditions to obtain a pyromellitic acid solution; the molar ratio of pyromellitic acid to DMF in step 1 and 2 is (1 mmol to 3 mol): (20 mL to 60 mL).

4. The method for preparing MOF-derived A-site doped ABO3-type perovskite material according to claim 1, characterized in that... The volume ratio of the cobalt salt solution to the trimesic acid solution mentioned in step 1③ is (20mL~60mL):(20mL~60mL); the stirring time mentioned in step 1③ is 10min~20min.

5. The method for preparing MOF-derived A-site doped ABO3 perovskite material according to claim 1, characterized in that... The hydrothermal reaction in step 1③ is carried out at a temperature of 150℃~180℃ for 10h~16h. In step 1③, the reaction product is centrifuged and washed 3 to 5 times with anhydrous ethanol, and then vacuum dried at 60℃~70℃ for 10h~12h to obtain the MOF matrix.

6. The method for preparing MOF-derived A-site doped ABO3 perovskite material according to claim 1, characterized in that... The amount of nitrate of the A-site element of the two ABO3 perovskites mentioned in step 2① is in the volume ratio of 1 mmol:(20 mL to 60 mL) to deionized water.

7. The method for preparing MOF-derived A-site doped ABO3 type perovskite material according to claim 1, characterized in that... The mass ratio of the MOF matrix to the volume of deionized water in step 2② is (300mg~600mg):(30mL~60mL).

8. The method for preparing MOF-derived A-site doped ABO3 perovskite material according to claim 1, characterized in that... The settling time in step 2.③ is 30–240 min; in step 2.③, the precipitate is washed with ethanol 3–5 times, and then vacuum dried at 60℃–70℃ for 10–12 h to obtain the MOF-based composite material with hydroxide precipitate on the outside.

9. The method for preparing MOF-derived A-site doped ABO3 perovskite material according to claim 1, characterized in that... The heating rate described in step three is 2℃ / min to 10℃ / min.

10. The application of the MOF-derived A-site doped ABO3 perovskite material prepared by the preparation method according to claim 1, characterized in that... MOF-derived A-site doped ABO3 perovskite materials are used as microwave absorbing materials.

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