Electromagnetic wave absorbing material with heteroatom defect constructed by metal organic framework and preparation method of electromagnetic wave absorbing material

Abstract

The invention relates to the technical field of electromagnetic wave absorbing materials, in particular to an electromagnetic wave absorbing material with heteroatom defects constructed by a metal organic framework and a preparation method of the electromagnetic wave absorbing material. Through construction of defect engineering, halogen atoms are introduced into the MOF, dipoles are formed, the polarization phenomenon of the dipoles is enhanced, asymmetric structures such as vacancies and dislocations are formed, and the asymmetric structures serve as additional polarization centers, so that dielectric polarization relaxation loss is remarkably enhanced; glucose is coated, a conductive network is constructed, the conductivity loss is improved, and the electromagnetic wave absorption capacity is improved. According to the technical scheme, firstly, a metal organic framework material with structural defects is synthesized through a solvent method; dispersing the synthesized MOF rich in defects in a water solution of glucose, and stirring to enable the MOF rich in defects to be self-polymerized on the surface of the MOF; and finally, pyrolyzing and carbonizing the glucose-coated defective MOF to obtain the final electromagnetic wave absorbing material.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic wave absorbing materials technology, specifically to a metal-organic framework structure with heteroatom defects for electromagnetic wave absorbing materials and its preparation method. Background Technology

[0002] With the continuous innovation of modern communication equipment and military stealth technology, a large number of electronic and electrical devices have developed rapidly. While bringing great convenience and improvement to people's lives and national military capabilities, they have also brought about problems related to electromagnetic radiation and information security. Reducing electromagnetic interference, minimizing environmental harm, and ensuring military information security have become the primary issues that urgently need to be addressed in the field of electromagnetic wave absorption.

[0003] Electromagnetic wave absorbing materials are one of the most effective solutions for suppressing and reducing electromagnetic problems. Currently, the single design concept of pursuing electromagnetic wave absorption can no longer meet people's needs; developing "thin, light, wide, and strong" electromagnetic wave absorbing materials represents the optimal characteristics sought in the field of electromagnetic wave absorption.

[0004] Traditional microwave absorbing materials, such as ferro-based materials and metal powders, suffer from bottlenecks such as high density, narrow bandwidth, and impedance mismatch. Hollow structures with excellent cavity structures and large specific surface areas are beneficial for modulating the conductivity and polarization relaxation of electromagnetic waves. They also allow for multiple reflections and scattering of electromagnetic waves within the material, thus dissipating electromagnetic wave energy. Generally, carbon materials have low density and high carrier mobility; common carbon nanotubes and graphene, for example, possess considerable electromagnetic wave absorption capabilities. However, their high conductivity leads to impedance mismatch, making it difficult for electromagnetic waves to penetrate the material surface and hindering more effective electromagnetic wave dissipation.

[0005] Metal-organic frameworks (MOFs) are formed by the chemical coordination of metal ions or metal clusters with suitable ligands. Due to their tunable and diverse compositions, unique porous morphologies, varied structural forms, and controllable specific surface areas, they have shown great potential in the field of electromagnetic wave absorption. The high porosity of MOFs is partially retained after pyrolysis. During pyrolysis, the breaking of organic bonds creates a large number of vacancies and hollow structures. Although this gives them an advantage over other microwave absorbing materials, their intrinsic polarization loss capability is often insufficient.

[0006] Publication No. CN 108834389 B discloses a method for preparing a bimetallic organic framework-derived porous carbon / multi-walled carbon nanotube nanocomposite microwave absorbing material. Using multi-walled carbon nanotubes as a carrier, cobalt nitrate hexahydrate and zinc nitrate hexahydrate as metal salt precursors, 2-methylimidazole as an organic ligand, and methanol and ethanol as a mixed solvent, the porous carbon / multi-walled carbon nanotube nanocomposite material is prepared by high-temperature pyrolysis. Publication No. CN 114727576 A discloses a metal-organic framework / conductive polymer-derived nanomaterial with electromagnetic wave absorption properties, its preparation method, and its applications. This metal-organic framework / conductive polymer-derived nanomaterial includes a first carbon structure, a second carbon structure, and a metal element. The first carbon structure has a network structure and is formed by the pyrolysis of conductive polyaniline. The second carbon structure and the metal element are formed by the pyrolysis of the metal-organic framework, with the metal element dispersed in the second carbon structure. The overall structure formed by the second carbon structure and the metal element is loaded on the first carbon structure. The problem is that it uses carbon nanotube materials, but due to their high conductivity, impedance mismatch occurs, making it difficult for electromagnetic waves to penetrate the material surface and thus preventing electromagnetic wave dissipation. Summary of the Invention

[0007] In view of this, the present invention provides a metal-organic framework (MOF) with heteroatom defects for use in electromagnetic wave absorbing materials and a method thereof. Through defect engineering, halogen atoms are introduced into the MOF to form dipoles, enhance dipole polarization, and form asymmetric structures such as vacancies and dislocations as additional polarization centers, which significantly enhances dielectric polarization relaxation loss. Coating glucose constructs a conductive network, improves conductivity loss, and enhances electromagnetic wave absorption capability.

[0008] To address the technical problems existing in the prior art, the present invention adopts the following technical solution: a method for preparing metal-organic frameworks with heteroatom defects for use in electromagnetic wave absorbing materials. First, a metal-organic framework material with structural defects is synthesized using a solvent method; then, the synthesized defect-rich metal-organic framework material is dispersed in an aqueous solution of glucose, and stirred to allow it to self-polymerize on the surface of the metal-organic framework material; finally, the glucose-coated defective metal-organic framework material is pyrolyzed and carbonized to obtain the final electromagnetic wave absorbing material.

[0009] Furthermore, the specific steps are as follows: Step 1: First, weigh 0.025g-0.075g of 2,5-thiophene-2-carboxylic acid, 0.102g-0.306g of 5-methyltetrazolium, 0.16g-0.48g of zinc nitrate hexahydrate, and 0.03g-0.09g of pyrazine into a glass bottle, then add a mixed solution of methanol and N,N-dimethylacetamide in a volume ratio of 1:1, and stir to dissolve at room temperature. Add a modifier with a molar ratio of 1:1 to that in step 1 to 2,5-thiophene-2-carboxylic acid during stirring, and continue stirring until the solid is completely dissolved; Then add 0.1-0.3 ml of tetramethylammonium hydroxide to the solution, stir continuously, wrap two layers of tin foil around the mouth of the glass bottle to completely cover it, and place it in an oven to heat at 120°C for 30-48 hours. After cooling to room temperature, wash and filter with washing liquid, and dry at room temperature to obtain defect-rich metal-organic framework material A. Step 2: Mix the defect-rich metal-organic framework material A obtained in Step 1 with an aqueous solution of glucose, stir, and then place it in a 60°C oven for evaporation and drying to finally form a glucose-coated defect-rich MOF crystal material B. Step 3: Grind the glucose-coated defect-rich MOF crystal material B obtained in Step 2 into powder, place it in a ceramic boat and put it in a tube furnace for pyrolysis and carbonization under a nitrogen atmosphere, and finally obtain glucose-coated defect MOF electromagnetic wave absorbing material.

[0010] Further, the modulator mentioned in step 1 is 5-bromo-2-carboxythiophene, thiophene-2-carboxylic acid, or 2-chlorothiophene-5-carboxylic acid.

[0011] Furthermore, the stirring time in step 1 is 30 minutes.

[0012] Furthermore, in step 1, filtration is performed using vacuum filtration, and the washing solution is methanol and DMA, each used for washing 3 times.

[0013] Furthermore, in step 2, the mass ratio of the defect-rich metal-organic framework material A to glucose is 1:1, the glucose aqueous solution concentration is 0.1 mol / L, and the stirring time is 3 h.

[0014] Furthermore, in step 3, the grinding time is 30 minutes, the carbonization temperature in the tube furnace is 800℃, and the carbonization time is 2 hours.

[0015] The electromagnetic wave absorbing material prepared by the above method.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1) This invention incorporates halogen atoms into MOFs by competing with ligands and halogen ligands, thereby pre-constructing abundant heteroatom defects and CX bonds in the MOF precursor. The heteroatom defects and the formed polar functional groups are retained and transformed after pyrolysis, generating a large number of dipole polarization centers in the derived carbon material formed after pyrolysis and carbonization. Charge migration and redistribution occur in the electromagnetic field, enhancing polarization relaxation and further improving polarization loss.

[0017] 2) In step one of this invention, 2,5-thiophene-2-carboxylic acid and 5-methyltetrazazole are used as ligands. The subsequent addition of 5-bromo-2-carboxythiophene, thiophene-2-carboxylic acid, or 2-chlorothiophene-5-carboxylic acid replaces part of the position of 2,5-thiophene-2-carboxylic acid. Due to the strong electronegativity of halogen atoms, differences arise in their coordination ability and spatial configuration with zinc ions. This difference leads to coordination competition during crystal growth, disrupting the original coordination lattice structure and introducing numerous coordination defects and dislocation defects. The introduction of halogen atoms constructs strong dipoles. Bromine atoms, with their strong electronegativity and large atomic radius, exhibit significant steric hindrance, interfering with normal crystal growth. The formed C-Br bonds simultaneously enhance the interfacial polarization positions, strengthening interfacial polarization. The high electronegativity and small radius of chlorine atoms result in weaker steric hindrance and limited defect-inducing ability, leading to lower polarization loss compared to bromine atoms and thus weaker electromagnetic wave absorption. Hydrogen atoms, with their smallest radius and weakest defect-inducing ability, contribute the least to polarization and are prone to impedance mismatch. Within the system, the construction of heteroatom defects enhances dipole polarization, while the formation of polar bonds strengthens interfacial polarization. Both factors jointly promote polarization relaxation and enhance defect polarization, further improving the polarization loss capability of the metal-organic framework (MOF). Simultaneously, pyrazine acts as a template agent, using non-bonded interactions to regulate the pore structure and morphology of the MOF. Tetramethylammonium hydroxide, as a mineralizer, promotes crystal growth with minimal addition. The resulting MOF possesses a porous framework and abundant porous structure, while the low density of carbon materials lays the foundation for its lightweight nature.

[0018] 3) After preparing the metal-organic framework (MOF) material, this invention further coats the crystal with a glucose polymer. During the evaporation process, the glucose undergoes dehydration condensation, forming a uniform polymer-carbon precursor coating interface layer on the defective MOF surface. Following pyrolysis and carbonization, this uniform polymer-carbon precursor coating interface layer transforms into a carbon shell structure, which serves to connect the MOF crystal particles and construct a continuous conductive network, enhancing conductivity and reducing carbon loss. Simultaneously, it improves carbon retention and protects against defects. This invention combines internal and external elements, with the synergistic effects of interface polarization, polarization defects, porous structure, and conductive network, enabling effective control of the composite dielectric constant and optimization of impedance matching and polarization through a multi-scale structure.

[0019] 4) Electromagnetic wave absorption performance tests were conducted using the material prepared according to this invention, revealing strong reflection loss and a wide effective absorption bandwidth. The heteroatom defects constructed using the metal-organic framework of this invention, when applied to electromagnetic wave absorbing materials with a thickness of 2.22 mm, achieve a minimum reflection loss of -17.23 dB. At a thickness of 2.80 mm, the maximum absorption bandwidth is 7.047 GHz, and the effective absorption bandwidth ranges from 10.87 GHz to 17.92 GHz, covering half of the X-band and almost the entire Ku-band. Attached Figure Description

[0020] Figure 1 This is a flowchart of the method for preparing defect-rich microwave absorbing materials according to the present invention (hydrothermal synthesis → glucose coating → high-temperature carbonization). Figure 2 This is the XRD pattern (matched to a standard card) of the defect-rich metal-organic framework material in this invention. Figure 3 This is a diagram showing the reflection loss of the metal-organic framework structure heteroatom defects used in electromagnetic wave absorbing materials in this invention. Figure 4 This invention relates to the application of heteroatom defects in metal-organic frameworks to electromagnetic wave absorbing materials at different thicknesses, as shown in the bandwidth diagrams. Figure 5 This is a diagram showing the real part ε' of the dielectric loss of the metal-organic framework structure heteroatom defects used in electromagnetic wave absorbing materials in this invention. Figure 6 This is a diagram showing the imaginary part ε" of the dielectric loss of the metal-organic framework structure heteroatom defects used in electromagnetic wave absorbing materials in this invention. Figure 7 The tangent of the dielectric loss, Tanδ, of the metal-organic framework structure heteroatom defects used in this invention for electromagnetic wave absorbing materials is... ε picture; Figure 8 This is a graph showing the real part μ' of the magnetic loss of the metal-organic framework structure heteroatom defects used in electromagnetic wave absorbing materials in this invention; Figure 9 This is a diagram showing the imaginary part μ" of the magnetic loss of the metal-organic framework structure heteroatom defects used in electromagnetic wave absorbing materials in this invention; Figure 10 The tangent of the magnetic loss, Tanδ, in the metal-organic framework structure heteroatom defects used in this invention for electromagnetic wave absorbing materials is... μ picture. Detailed Implementation

[0021] To further understand the present invention, the present invention will be described below with reference to embodiments. These descriptions are only for further explaining the features and advantages of the present invention and are not intended to limit the claims of the present invention. Example

[0022] This invention discloses a method for preparing electromagnetic wave absorbing materials using heteroatom defects in metal-organic framework structures. Figure 1 As shown, it includes the following steps: (1) Weigh 2,5-thiophene-2-carboxylic acid (0.45 mmol, 0.075 g), zinc nitrate hexahydrate (1.62 mmol, 0.48 g), pyrazine (0.09 g) and 5-methyltetrazole (3.6 mmol, 0.306 g) into a glass bottle, and then add a mixed solution of methanol (9 ml) and N,N-dimethylacetamide (9 ml), and stir to dissolve at room temperature for 30 min; Add 5-bromo-2-carboxythiophene (0.45 mmol, 0.090 g) while stirring, and continue stirring until the solid is completely dissolved. Finally, add 0.3 ml of tetramethylammonium hydroxide to the solution, stir continuously for 30 min, wrap the mouth of the glass bottle with two layers of tin foil, completely cover it, put it in an oven and heat it at 120 °C for 48 h, cool it to room temperature, wash and filter it three times each with methanol and DMA solution, and dry it at room temperature to obtain defect-rich metal-organic framework material A. (2) The defect-rich metal-organic framework material A obtained in step 1 is mixed with glucose solid at a mass ratio of 1:1 and the concentration of glucose aqueous solution is 0.1 mol / L. First, 55 ml of water is weighed, 1 g of glucose solid is added and stirred for 10 min, then 1 g of material A is added and stirred for 3 h. The mixture is then placed in a 60 °C oven for evaporation and drying for 30 min, and finally glucose-coated defect MOF crystal material B is formed. (3) Grind the glucose-coated defect-rich MOF crystal material B obtained in step 2 into powder, put it into a ceramic boat and place it in a tube furnace. Under a nitrogen atmosphere, perform pyrolysis carbonization at 800°C for two hours to finally obtain glucose-coated defect MOF electromagnetic wave absorbing material.

[0023] Example 2: The difference from Example 1 is that thiophene-2-carboxylic acid is used as a modulator, and the amount used is 0.45 mmol, 0.057 g, and hydrogen atoms are introduced as defect atoms.

[0024] Example 3: The difference from Example 1 is that 2-chlorothiophene-5-carboxylic acid is used as a modifier, and the amount used is 0.45 mmol, 0.072 g, and chlorine atoms are introduced as defect atoms.

[0025] Example 4: The difference from Example 1 is that the overall amount of material used is reduced.

[0026] This invention discloses a method for preparing electromagnetic wave absorbing materials using heteroatom defects in metal-organic framework structures. Figure 1As shown, it includes the following steps: (1) Weigh 2,5-thiophene-2-carboxylic acid (0.290 mmol, 0.050 g), zinc nitrate hexahydrate (1.08 mmol, 0.32 g), pyrazine (0.06 g), and 5-methyltetrazole (2.4 mmol, 0.204 g) into a glass bottle, then add a mixed solution of methanol (6 ml) and N,N-dimethylacetamide (6 ml), and stir to dissolve at room temperature for 30 min; during stirring, add 5-bromo-2-carboxythiophene (0.435 mmol, 0.060 g). Example 4: The difference from Example 1 is that Example 4 is a defect crystal prepared by reducing the overall content by three times based on Example 1. (1) Weigh 2,5-thiophene-2-carboxylic acid (0.15 mmol, 0.025 g), zinc nitrate hexahydrate (0.54 mmol, 0.16 g), pyrazine (0.03 g) and 5-methyltetrazole (1.2 mmol, 0.102 g) into a glass bottle, and then add a mixed solution of methanol (3 ml) and N,N-dimethylacetamide (3 ml), and stir to dissolve at room temperature for 30 min; Add 5-bromo-2-carboxythiophene (0.15 mmol, 0.030 g) while stirring, and continue stirring until the solid is completely dissolved. Finally, add 0.1 ml of tetramethylammonium hydroxide to the solution, stir continuously for 30 min, wrap the mouth of the glass bottle with two layers of tin foil, completely cover it, put it in an oven and heat it at 120 °C for 48 h, cool it to room temperature, wash and filter it three times each with methanol and DMA solution, and dry it at room temperature to obtain defect-rich metal-organic framework material A. (2) The defect-rich metal-organic framework material A obtained in step 1 is mixed with glucose solid at a mass ratio of 1:1 and the concentration of glucose aqueous solution is 0.1 mol / L. First, 55 ml of water is weighed, 1 g of glucose solid is added and stirred for 10 min, then 1 g of material A is added and stirred for 3 h. The mixture is then placed in a 60 °C oven for evaporation and drying for 30 min, and finally glucose-coated defect MOF crystal material B is formed. (3) Grind the glucose-coated defect-rich MOF crystal material B obtained in step 2 into powder, put it into a ceramic boat and place it in a tube furnace. Under a nitrogen atmosphere, perform pyrolysis carbonization at 800°C for two hours to finally obtain glucose-coated defect MOF electromagnetic wave absorbing material.

[0027] Example 5: The difference from Example 1 is that Example 5 is a defect crystal prepared by doubling the overall content based on Example 4. The steps are as follows: (1) Weigh 2,5-thiophene-2-carboxylic acid (0.30 mmol, 0.050 g), zinc nitrate hexahydrate (1.08 mmol, 0.32 g), pyrazine (0.06 g) and 5-methyltetrazole (2.4 mmol, 0.204 g) into a glass bottle, and then add a mixed solution of methanol (6 ml) and N,N-dimethylacetamide (6 ml), and stir to dissolve at room temperature for 30 min; Add 5-bromo-2-carboxythiophene (0.30 mmol, 0.060 g) while stirring, and continue stirring until the solid is completely dissolved. Finally, 0.2 ml of tetramethylammonium hydroxide was added to the solution, and the mixture was stirred for 30 min. Then, two layers of tin foil were wrapped around the mouth of the glass bottle to completely cover it. The bottle was then placed in an oven and heated at 120 °C for 48 h. After cooling to room temperature, the bottle was washed and filtered three times each with methanol and DMA solution. Finally, the bottle was dried at room temperature to obtain a defect-rich metal-organic framework material A. (2) The defect-rich metal-organic framework material A obtained in step 1 is mixed with glucose solid at a mass ratio of 1:1 and the concentration of glucose aqueous solution is 0.1 mol / L. First, 55 ml of water is weighed, 1 g of glucose solid is added and stirred for 10 min, then 1 g of material A is added and stirred for 3 h. The mixture is then placed in a 60 °C oven for evaporation and drying for 30 min, and finally glucose-coated defect MOF crystal material B is formed. (3) Grind the glucose-coated defect-rich MOF crystal material B obtained in step 2 into powder, put it into a ceramic boat and place it in a tube furnace. Under a nitrogen atmosphere, perform pyrolysis carbonization at 800°C for two hours to finally obtain glucose-coated defect MOF electromagnetic wave absorbing material.

[0028] Based on the synthesis process of Examples 1-5 and the electromagnetic wave absorption performance test results, it can be concluded that the optimal scheme is to increase the overall content by three times and to use 5-bromo-2-carboxythiophene as the modulator of doped halogen atoms in Example 1. Therefore, crystals can be successfully synthesized and the amount of crystals synthesized is larger. Furthermore, due to the strong electronegativity and large atomic radius of bromine, the generation of defects is enhanced, and the formed C-Br polar bonds provide dipole polarization for the material, further strengthening polarization loss. The following are the test results for the electromagnetic wave absorbing material prepared in Example 1: like Figure 2 This is the XRD pattern of the metal-organic framework heteroatom defect crystal material synthesized at three times the concentration in this invention. By comparing it with the standard spectrum, it can be observed that the two are basically consistent, indicating that the metal-organic framework heteroatom defect crystal material was successfully synthesized at three times the concentration.

[0029] like Figure 3This is a graph showing the reflection loss (RL) values ​​of the metal-organic framework structure with heteroatom defects used in the electromagnetic wave absorbing material at different thicknesses. It can be seen that at 2.22 mm, the reflection loss value of the metal-organic framework structure with heteroatom defects used in the electromagnetic wave absorbing material reaches -17.23 dB, indicating that the material has good electromagnetic wave absorption performance.

[0030] like Figure 4 This invention relates to a metal-organic framework structure with heteroatom defects used in electromagnetic wave absorbing materials at different thicknesses, showing bandwidth band diagrams. At 2.80 mm, the effective absorption bandwidth is 10.87 GHz to 17.92 GHz, covering half of the X-band and almost the entire Ku-band.

[0031] like Figure 5 This is a real part diagram of the dielectric loss of the metal-organic framework structure heteroatom defects prepared in this invention for use in electromagnetic wave absorbing materials. The real part of the dielectric constant (ε') decreases gradually in the range of 2 GHz to 18 GHz.

[0032] like Figure 6 This is an imaginary part diagram of the dielectric loss of the metal-organic framework structure heteroatom defects prepared in this invention for use in electromagnetic wave absorbing materials. The imaginary part of the dielectric constant (ε") gradually decreases within the range of 2 GHz to 18 GHz.

[0033] like Figure 7 This is a tangent diagram of the dielectric loss of the metal-organic framework structure with heteroatom defects prepared in this invention, used in electromagnetic wave absorbing materials. The tangent of the dielectric loss (Tanδ) ε =ε" / ε') decreases slowly in the range of 2 GHz to 18 GHz, just like the real and imaginary parts of the dielectric constant.

[0034] like Figure 8 This is a real part diagram of the magnetic loss of the metal-organic framework structure heteroatom defects prepared in this invention for use in electromagnetic wave absorbing materials. The real part value (μ') of the magnetic loss remains above 1 throughout the entire frequency range of 2 GHz to 18 GHz.

[0035] like Figure 9 This is an imaginary part diagram of the magnetic loss of the metal-organic framework structure heteroatom defects used in electromagnetic wave absorbing materials prepared in this invention. The imaginary part value (μ") of the magnetic loss oscillates across the entire frequency range of 2GHz to 18GHz, but shows an overall decreasing trend.

[0036] like Figure 10 This is a tangent diagram of the magnetic loss of the metal-organic framework structure with heteroatom defects prepared in this invention, used in electromagnetic wave absorbing materials. The tangent of the magnetic loss (Tanδ) μ =μ" / μ') shows an oscillating decrease in the range of 2GHz to 18GHz, and finally the value is basically stable at around 0.

[0037] Combination Figures 1-10 As a result, this material exhibits excellent performance in electromagnetic wave absorption tests. Figure 3 As shown, when the matching thickness is 2.22 mm, the material's reflection loss reaches -17.23 dB, indicating its strong attenuation capability. Figure 4 As shown, with a thickness of 2.80 mm, the material's effective absorption bandwidth (RL < -10 dB) covers the frequency band from 10.87 GHz to 17.92 GHz, covering half of the X-band and almost the entire Ku-band, exhibiting wideband absorption characteristics. This can be seen from the basic electromagnetic parameters, such as... Figures 5 to 7 Throughout the 2-18 GHz frequency range, both the real part (ε') and the imaginary part (ε") of the final material dielectric constant exhibit a gradual decreasing trend, and the dielectric loss tangent (tan δ) remains constant. e The synchronous and slow decline demonstrates that the polar losses caused by heteroatom defects and polar bonds play a major role in the overall material loss mechanism. Figures 8 to 10 The real part of the material's permeability (μ') remains stable above 1 throughout the entire test frequency band, while the imaginary part of the permeability (μ'') and the magnetic loss tangent (tan δ) are relatively stable. m The dielectric loss exhibits a fluctuating downward trend, eventually approaching zero in some high-frequency regions. This indicates that the material composition provides a certain degree of magnetic loss capability, but dielectric loss is still the dominant factor, with both components working together to promote electromagnetic wave absorption.

[0038] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not describe all details exhaustively, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification.

[0039] These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing electromagnetic wave absorbing materials using heteroatom defects constructed from metal-organic frameworks, characterized in that, First, a metal-organic framework material with structural defects is synthesized using a solvent method. Then, the synthesized defect-rich metal-organic framework material is dispersed in an aqueous solution of glucose, and stirred to allow it to self-polymerize on the surface of the metal-organic framework material. Finally, the glucose-coated defective metal-organic framework material is pyrolyzed and carbonized to obtain the final electromagnetic wave absorbing material.

2. The method for preparing a metal-organic framework structure with heteroatom defects for electromagnetic wave absorbing materials according to claim 1, characterized in that, The specific steps are as follows: Step 1: First, weigh 0.025g-0.075g of 2,5-thiophene-2-carboxylic acid, 0.102g-0.306g of 5-methyltetrazolium, 0.16g-0.48g of zinc nitrate hexahydrate, and 0.03g-0.09g of pyrazine into a glass bottle, then add a mixed solution of methanol and N,N-dimethylacetamide in a volume ratio of 1:1, and stir to dissolve at room temperature. Add a modifier with a molar ratio of 1:1 to that in step 1 to 2,5-thiophene-2-carboxylic acid during stirring, and continue stirring until the solid is completely dissolved; Then add 0.1-0.3 ml of tetramethylammonium hydroxide to the solution, stir continuously, wrap two layers of tin foil around the mouth of the glass bottle to completely cover it, and place it in an oven to heat at 120°C for 30-48 hours. After cooling to room temperature, wash and filter with washing liquid, and dry at room temperature to obtain defect-rich metal-organic framework material A. Step 2: Mix the defect-rich metal-organic framework material A obtained in Step 1 with an aqueous solution of glucose, stir, and then place it in a 60°C oven for evaporation and drying to finally form a glucose-coated defect-rich MOF crystal material B. Step 3: Grind the glucose-coated defect-rich MOF crystal material B obtained in Step 2 into powder, place it in a ceramic boat and put it in a tube furnace for pyrolysis and carbonization under a nitrogen atmosphere, and finally obtain glucose-coated defect MOF electromagnetic wave absorbing material.

3. The method for preparing a metal-organic framework structure with heteroatom defects for electromagnetic wave absorbing materials according to claim 2, characterized in that, The modifier in step 1 is 5-bromo-2-carboxythiophene, thiophene-2-carboxylic acid, or 2-chlorothiophene-5-carboxylic acid.

4. The method for preparing a metal-organic framework structure with heteroatom defects for electromagnetic wave absorbing materials according to claim 3, characterized in that, The stirring time in step 1 is 30 minutes.

5. The method for preparing a metal-organic framework structure with heteroatom defects for electromagnetic wave absorbing materials according to claim 4, characterized in that, In step 1, filtration is performed by suction filtration, and the washing solution is methanol and DMA, each used for washing 3 times.

6. The method for preparing a metal-organic framework structure with heteroatom defects for electromagnetic wave absorbing materials according to claim 2, characterized in that, In step 2, the mass ratio of defect-rich metal-organic framework material A to glucose is 1:1, the glucose aqueous solution concentration is 0.1 mol / L, and the stirring time is 3 h.

7. The method for preparing a metal-organic framework structure with heteroatom defects for electromagnetic wave absorbing materials according to claim 2, characterized in that, In step 3, the grinding time is 30 minutes, the carbonization temperature in the tube furnace is 800°C, and the carbonization time is 2 hours.

8. The electromagnetic wave absorbing material prepared by the preparation method according to claim 1.

Images