Preparation method of magnetic trimetal MOF / AHF-5 composite polyurethane wave-absorbing film

Abstract

The invention discloses a preparation method of a magnetic trimetal MOF / AHF-5 composite polyurethane wave-absorbing film, which comprises the following steps: firstly, synthesizing a metal organic framework material by using a hydrothermal method, and doping a hybrid crystalline metal organic framework containing iron, cobalt and nickel trimetals by stirring; the chemical composition of a polymer crystalline precursor is regulated and controlled by regulating and controlling the proportion of iron, cobalt and nickel metals, the magnetic trimetal MOF is loaded in a uniformly growing nanofiber membrane through an electrostatic spinning technology, interface polarization of the metal-doped MOF and the nanofiber membrane is realized, and a channel is provided for energy transmission and charge transfer by layer-by-layer interweaving and winding of fibers. Multiple scattering of microwaves in the material is increased; and carbonizing, and mixing with polyurethane to obtain the tri-metal MOF wave-absorbing film. The magnetic performance of the fiber is remarkably improved, and the advantages of high saturation magnetization and strong magnetic coupling are brought, so that the wave absorbing performance of the membrane is enhanced.

Description

Technical Field

[0001] The invention belongs to the technical field of electromagnetic wave absorbing materials, and particularly relates to a method for preparing a magnetic tri-metal MOF / AHF-5 composite polyurethane absorbing film. Background Art

[0002] Today, electronic communication devices are ubiquitous in every area of ​​our lives, making our lives more convenient. However, the harm caused by electromagnetic waves emitted by these devices cannot be underestimated. The electromagnetic radiation caused by a large amount of electromagnetic waves poses a challenge to our information security and also causes certain problems for human health. Therefore, research on the effective absorption and attenuation of electromagnetic waves is particularly important and has great practical significance.

[0003] Electromagnetic absorbers need to convert incident electromagnetic wave energy into heat or other energies. This requires both impedance matching and attenuation properties. Impedance matching requires that the surface impedance of the absorber match that of the free space through which the electromagnetic wave propagates, minimizing reflection of the wave itself. Attenuation, on the other hand, requires that the absorber convert the electromagnetic wave energy into other energy dissipations through its own internal dielectric and magnetic losses. Therefore, metal-organic frameworks (MOFs) offer significant advantages for the preparation of absorbers. MOFs are renowned for their porous structure and high surface area, providing numerous interfaces for electromagnetic wave absorption and increasing the number of interaction sites between the wave and the material. MOFs also possess functional properties. MOFs possess diverse structures, allowing for the formation of numerous MOF materials by combining different metal ions and ligands. Surface modification, such as the introduction of various metal groups and conductive functional groups, can enhance magnetic and dielectric loss. Electrospinning technology, on the other hand, creates a three-dimensional, porous network by producing nanofibers. The large number of interfaces between fibers enhances interfacial polarization losses, while the pore structure optimizes impedance matching and reduces reflection. Electrospinning can be used to produce MOF nanofibers containing MOF microparticles. Polyurethane, as a binder, possesses the elasticity of rubber and the strength of plastic. By manipulating the matrix and filler, good impedance matching and the synergistic effects of multiple high-loss mechanisms can be achieved. These three factors work together to enhance electromagnetic absorption performance. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing a magnetic trimetallic MOF / AHF-5 composite polyurethane absorbing film, which solves the problem of insufficient absorbing performance of existing materials through fiber nano-sizing, ligand functionalization and multi-metal synergy.

[0005] The first technical solution adopted by the present invention is a method for preparing a magnetic trimetallic MOF / AHF-5 composite polyurethane absorbing film. The method first uses a hydrothermal method to synthesize a metal-organic framework material, and then stir-dopes a hybrid crystalline metal-organic framework containing three metals: iron, cobalt, and nickel. The chemical composition of the polymer crystalline precursor is regulated by adjusting the ratio of iron, cobalt, and nickel metals. The magnetic trimetallic MOF is loaded into a uniformly grown nanofiber membrane through electrospinning technology, and then carbonized and mixed with polyurethane to obtain the trimetallic MOF absorbing film. The specific operating steps are as follows: Step 1, adding Zn(oAC)2·H2O, 5-amino-1H-tetrazole, and pyromellitic acid to deionized water, and pouring the mixture into a polytetrafluoroethylene-lined autoclave to form a mixed solution; stirring the mixed solution at room temperature, and simultaneously adding sodium hydroxide to adjust the pH value to 6-7; placing the mixture into a reactor, and placing it in an oven for heating and reaction, cooling and removing the mixture after the reaction is completed; washing with deionized water and ethanol, filtering and collecting to obtain AHF-5 crystals, and drying in air to finally obtain crystalline AHF-5 powder; Step 2: Iron, Cobalt, and Nickel Trimetallic Doping Ferric chloride, cobalt acetate, and nickel acetate are mixed and added to ethanol to obtain a mixed solution; the mixed solution is stirred, and crystalline AHF-5 powder is added to the solution during the stirring process. After the crystalline AHF-5 powder is added, the solution is continuously stirred until the ethanol is completely evaporated and stirred to dryness, thereby obtaining an iron-cobalt-nickel trimetallic doped MOF composite material; Step 3: dissolving polyacrylonitrile powder in N,N-dimethylformamide to obtain a PAN solution; grinding the iron, cobalt, and nickel trimetallic MOF composite material into powder, adding it to the PAN solution and stirring, and then ultrasonically dispersing it until the solution is uniform to obtain a trimetallic MOF / PAN spinning solution; electrospinning the trimetallic MOF / PAN spinning solution to obtain a trimetallic MOF / PAN nanofiber membrane; Step 4: High temperature carbonization The obtained tri-metallic MOF / PAN nanofiber membrane was placed into a porcelain boat under a nitrogen atmosphere and placed in a tubular furnace for carbonization annealing. Polyurethane was selected as a binder, and the carbonized nanofiber membrane was mixed with polyurethane under vacuum drying to obtain a tri-metallic MOF absorbing membrane. The present invention is also characterized in that: The Zn(oAC)2·H2O in step 1 can be replaced by zinc acetate or zinc nitrate.

[0006] In step 1, the molar ratio of sodium hydroxide to Zn(oAC)2·H2O, 5-amino-1H-tetrazolyl and pyromellitic acid is 6:2:2:1.

[0007] In step 1, the heating temperature is 160° C. to 170° C., and the reaction time is 36 h to 40 h.

[0008] In step 1, the filtration was performed by suction filtration, and the product was washed three times with deionized water and ethanol respectively.

[0009] The ferric chloride, cobalt acetate and nickel acetate in step 2 can be replaced by corresponding iron, cobalt and nickel salts; the mass ratio of single metal iron, cobalt and nickel in the ferric chloride, cobalt acetate and nickel acetate is 1:1:1.

[0010] The mass of the tri-metal doped MOF composite material in step 3 is 5%-10% of the mass of the polyacrylonitrile.

[0011] In step 4, the annealing temperature is 800° C. and the annealing time is 2 hours.

[0012] The mass ratio of the polyurethane in step 4 to the tri-metallic MOF / PAN nanofiber membrane before annealing in step 3 is 6:1.

[0013] The synthesis principle of the key steps in the present invention is: A novel zinc salt porous high-surface-to-weight ratio material (AHF-5) was synthesized hydrothermally using 5-amino-1H-tetrazole and pyromellitic acid as ligands, followed by the addition of Zn(oAC)2·H2O. The magnetic iron, cobalt, and nickel trimetallic metals were loaded onto the MOF surface, and then electrospinning was used to prepare a nanofiber membrane. The trimetallic MOF was evenly distributed at the interwoven interface of the fiber membrane. The membrane was then carbonized by high-temperature pyrolysis to form carbon nanofibers. The azole ligands within the MOF formed a carbon-based composite containing carbon nitride, enhancing the composite's electrical conductivity.

[0014] The beneficial effects of the present invention are: (1) Adjustable operation and synergistic effect: The electrospinning preparation method is simple and the operating parameters are easy to control. The fiber membrane has excellent appearance and morphology, the fiber layers are evenly distributed, the nanofibers have uniform diameters, and the interweaving of the fiber layers provides a channel for energy transmission and charge transfer, increasing the multiple scattering of microwaves inside the material. The synergistic effect of the doped trimetallic MOF significantly improves the magnetic properties of the fiber, bringing the advantages of high saturation magnetization and strong magnetic coupling, thereby enhancing the membrane's microwave absorption performance.

[0015] (2) Simple process and mass production: Applicable to various raw materials such as zinc salts (zinc acetate, zinc nitrate), cobalt nickel salts (chloride, sulfate). After the AHF-5 crystals are synthesized by a simple hydrothermal method, they are then doped with iron, cobalt and nickel trimetallics by simple stirring, and finally converted into a carbon-based composite trimetallic MOF material containing carbon nitride during the final heat treatment process. The absorption properties of the iron, cobalt and nickel doped MOF material can be easily controlled by varying the doping amount of the trimetallics. When synthesizing AHF-5 crystals, the amount of reactants can be multiplied to increase the amount of the synthesized reaction product crystals.

[0016] (3) High reflection loss and wide bandwidth: This invention provides a synthetic strategy for preparing a magnetic trimetallic MOF composite polyurethane absorbing film using electrospinning technology. The absorption performance test of this material shows extremely strong reflection loss and a wide effective absorption bandwidth. The magnetic trimetallic MOF composite polyurethane absorbing film (FeCoNi-AHF-5 / PAN@C) prepared by electrospinning has a minimum reflection loss of -66.39dB at a thickness of 2.4mm. At a thickness of 1.63mm, the effective absorption bandwidth is 13.08GHz~18GHz, covering the vast majority of the Ku band. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a flow chart of the preparation method of the composite absorbing material of the present invention (hydrothermal synthesis → metal doping → electrospinning → high-temperature carbonization); Figure 2 is the XRD pattern of the AHF-5 crystalline material in the present invention (matching the standard card); Figure 3 This is a graph showing the reflection loss value of the magnetic tri-metallic MOF composite polyurethane absorbing film prepared by the electrospinning technology of the present invention; Figure 4 This is the absorption bandwidth diagram of the magnetic tri-metallic MOF composite polyurethane absorbing film prepared by the electrospinning technology in the present invention; Figure 5 is a graph of the real part of the dielectric loss ε' of the magnetic tri-metallic MOF composite polyurethane absorbing film prepared by the electrospinning technology in the present invention; Figure 6 This is a graph showing the imaginary part of the dielectric loss ε" of the magnetic tri-metallic MOF composite polyurethane absorbing film prepared by electrospinning technology in the present invention; Figure 7 The tangent value of the dielectric loss Tanδ of the electrospinning technology used in the present invention to prepare the magnetic tri-metallic MOF composite polyurethane absorbing film ε picture; Figure 8 is a graph of the real part of the magnetic loss μ' of the magnetic tri-metallic MOF composite polyurethane absorbing film prepared by the electrospinning technology in the present invention; Figure 9 This is a graph showing the imaginary value μ" of the magnetic loss when the electrospinning technology is used to prepare the magnetic tri-metallic MOF composite polyurethane absorbing film in the present invention; Figure 10 is the tangent value of the magnetic loss Tanδ when the electrospinning technology in the present invention is used to prepare the magnetic tri-metal MOF composite polyurethane absorbing film μ picture. DETAILED DESCRIPTION

[0018] In order to further understand the present invention, the present invention is described below in conjunction with 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.

[0019] Example 1: The electrospinning technology of the present invention is used to prepare a method for preparing a magnetic tri-metal MOF composite polyurethane absorbing film, and the process is as follows: Figure 1 The specific steps are as follows: (1) Zinc acetate dihydrate (0.745 g, 2.5 mmol), 5-amino-1H-tetrazole (0.215 g, 2.5 mmol), and pyromellitic acid (0.32 g, 1.25 mmol) were added to deionized water (10 ml) and poured into a polytetrafluoroethylene-lined autoclave (20 ml) to form a solution; the solution was stirred at room temperature; sodium hydroxide (0.38) was added while stirring to adjust the pH value (6-7); the mixed solution was stirred and placed in a reactor, and placed in an oven at 170°C for 72 h, and then taken out after cooling to room temperature; the reacted crystals were washed three times with deionized water and ethanol solution respectively, and finally AHF-5 crystals were collected by filtration and dried in air to obtain crystalline powder; (2) Ferric chloride (0.033 g, 8.33%), cobalt acetate tetrahydrate (0.049 g, 8.33%), and nickel acetate tetrahydrate (0.049 g, 8.33%) were added to a beaker containing ethanol (10 ml) to obtain three mixed solutions. The three solutions were stirred on a stirrer, and AHF-5 crystal powder (1.2 g) was added to each solution during the stirring process. The solution after adding the crystal powder was stirred continuously until the ethanol was completely evaporated and dried to obtain an iron-cobalt-nickel trimetallic doped MOF composite material (FeCoNi-AHF-5).

[0020] (3) Add PAN (3 g) powder to a beaker containing DMF (20 g) and stir magnetically at room temperature until the powder is completely dissolved and the solution is evenly dispersed to obtain a PAN solution. Pour FeCoNi-AHF-5 (0.3 g) obtained in step (2) into a mortar and grind it evenly into powder. Add it to the above PAN solution and stir it on a stirrer for 4 hours. Then, perform ultrasonic dispersion for 30 minutes until it is dissolved to obtain a trimetallic MOF / PAN spinning solution. Use a 10 ml medical syringe to draw the above trimetallic MOF / PAN spinning solution, connect the needle, and place it on the spinning device. Adjust the parameters of the electrospinning device: the spinning flow rate is 1.2 ml / h, the distance between the receiving roller and the spinneret is about 18 cm, the voltage is 18 kV for electrospinning, and the roller speed is 800 rpm. A magnetic trimetallic MOF / PAN nanofiber membrane is obtained.

[0021] (4) The prepared magnetic trimetallic MOF / PAN nanofiber membrane was placed in a porcelain boat under a nitrogen atmosphere and carbonized in a tube furnace at 800°C for two hours to obtain a carbonized trimetallic MOF absorbent membrane. Waterborne polyurethane (2.4 g) was mixed with the carbonized trimetallic MOF absorbent membrane (0.4 g) and dried in a vacuum oven at 60°C before being processed into coaxial rings.

[0022] Example 2: (1) Zinc acetate dihydrate (0.745 g, 2.5 mmol), 5-amino-1H-tetrazole (0.215 g, 2.5 mmol), and pyromellitic acid (0.32 g, 1.25 mmol) were added to deionized water (10 ml) and poured into a polytetrafluoroethylene-lined autoclave (20 ml) to form a solution; the solution was stirred at room temperature; sodium hydroxide (0.38) was added while stirring to adjust the pH value (6-7); the mixed solution was stirred and placed in a reactor, and placed in an oven at 170°C for 72 h, and then taken out after cooling to room temperature; the reacted crystals were washed three times with deionized water and ethanol solution respectively, and finally AHF-5 crystals were collected by filtration and dried in air to obtain crystal powder; (2) Ferric chloride (0.033 g, 8.33%), cobalt acetate tetrahydrate (0.049 g, 8.33%), and nickel acetate tetrahydrate (0.049 g, 8.33%) were added to a beaker containing ethanol (10 ml) to obtain three mixed solutions. The three solutions were stirred on a stirrer, and AHF-5 crystal powder (1.2 g) was added to each solution during the stirring process. The solution after adding the crystal powder was stirred continuously until the ethanol was completely evaporated and dried to obtain an iron-cobalt-nickel trimetallic doped MOF composite material (FeCoNi-AHF-5).

[0023] (3) PAN (3 g) powder was added to a beaker containing DMF (20 g) and magnetically stirred at room temperature until the powder was completely dissolved and the solution was evenly dispersed to obtain a PAN solution. FeCoNi-AHF-5 (0.24 g) obtained in step (2) was poured into a mortar and evenly ground into a powder. The mixture was added to the above PAN solution and stirred on a stirrer for 4 hours. Ultrasonic dispersion was then performed for 30 minutes until dissolved to obtain a trimetallic MOF / PAN spinning solution. A 10 ml medical syringe was used to draw the above trimetallic MOF / PAN spinning solution, connected to a needle, and placed on a spinning device. The parameters of the electrospinning device were adjusted as follows: the spinning flow rate was 1.2 ml / h, the receiving roller was approximately 18 cm away from the spinneret, the voltage was 18 kV for electrospinning, and the roller speed was 800 rpm. A magnetic trimetallic MOF / PAN nanofiber membrane was obtained.

[0024] (4) The prepared magnetic trimetallic MOF / PAN nanofiber membrane was placed in a porcelain boat under a nitrogen atmosphere and carbonized in a tube furnace at 800°C for two hours to obtain a carbonized trimetallic MOF absorbent membrane. Waterborne polyurethane (2.4 g) was mixed with the carbonized trimetallic MOF absorbent membrane (0.4 g) and dried in a vacuum oven at 60°C before being processed into coaxial rings.

[0025] Example 3: (1) Zinc acetate dihydrate (0.745 g, 2.5 mmol), 5-amino-1H-tetrazole (0.215 g, 2.5 mmol), and pyromellitic acid (0.32 g, 1.25 mmol) were added to deionized water (10 ml) and poured into a polytetrafluoroethylene-lined autoclave (20 ml) to form a solution; the solution was stirred at room temperature; sodium hydroxide (0.38) was added while stirring to adjust the pH value (6-7); the mixed solution was stirred and placed in a reactor, and placed in an oven at 170°C for 72 h, and then taken out after cooling to room temperature; the reacted crystals were washed three times with deionized water and ethanol solution respectively, and finally AHF-5 crystals were collected by filtration and dried in air to obtain crystalline powder; (2) Ferric chloride (0.041 g, 10%), cobalt acetate tetrahydrate (0.051 g, 10%), and nickel acetate tetrahydrate (0.051 g, 10%) were added to a beaker containing ethanol (10 ml) to obtain three mixed solutions. The three solutions were stirred on a stirrer, and AHF-5 crystal powder (1.2 g) was added to each solution during the stirring process. The solution after adding the crystal powder was stirred continuously until the ethanol was completely evaporated and dried to obtain an iron-cobalt-nickel trimetallic doped MOF composite material (FeCoNi-AHF-5).

[0026] (3) Add PAN (3 g) powder to a beaker containing DMF (20 g) and stir magnetically at room temperature until the powder is completely dissolved and the solution is evenly dispersed to obtain a PAN solution. Pour FeCoNi-AHF-5 (0.3 g) obtained in step (2) into a mortar and grind it evenly into powder. Add it to the above PAN solution and stir it on a stirrer for 4 hours. Then, perform ultrasonic dispersion for 30 minutes until it is dissolved to obtain a trimetallic MOF / PAN spinning solution. Use a 10 ml medical syringe to draw the above trimetallic MOF / PAN spinning solution, connect the needle, and place it on the spinning device. Adjust the parameters of the electrospinning device: the spinning flow rate is 1.2 ml / h, the distance between the receiving roller and the spinneret is about 18 cm, the voltage is 18 kV for electrospinning, and the roller speed is 800 rpm. A magnetic trimetallic MOF / PAN nanofiber membrane is obtained.

[0027] (4) The prepared magnetic trimetallic MOF / PAN nanofiber membrane was placed in a porcelain boat under a nitrogen atmosphere and carbonized in a tube furnace at 800°C for two hours to obtain a carbonized trimetallic MOF absorbent membrane. Waterborne polyurethane (2.4 g) was mixed with the carbonized trimetallic MOF absorbent membrane (0.4 g) and dried in a vacuum oven at 60°C before being processed into coaxial rings.

[0028] Based on the synthesis processes of Examples 1-3 and the electromagnetic wave absorption performance test results, it can be concluded that in Example 1, a trimetallic MOF content of 10% of the PAN mass and a total trimetallic doping level of 25% are the most preferred. This optimal configuration achieves optimal synergy between the magnetic trimetallic MOF and the nanofibers, and they are evenly dispersed within them. In the electromagnetic wave absorption performance test of Example 1, the reflection loss of the magnetic trimetallic MOF (AHF-5) composite polyurethane absorbing film prepared using electrospinning technology at a thickness of 2.4 mm reached -66.39 dB. exist At 2.0 mm, the effective absorption bandwidth is 10.44 GHz to 14.16 GHz, covering parts of the Ku-band and X-band. At 1.63 mm, the effective absorption bandwidth is 13.08 GHz to 18 GHz, covering the vast majority of the Ku-band. This demonstrates that the prepared composite material has high absorption performance.

[0029] Example 4 Step 1, adding Zn(oAC)2·H2O, 5-amino-1H-tetrazole, and pyromellitic acid to deionized water, and pouring the mixture into a polytetrafluoroethylene-lined autoclave to form a mixed solution; stirring the mixed solution at room temperature, and simultaneously adding sodium hydroxide to adjust the pH value to 6; placing the mixture into a reactor, and heating the mixture in an oven at 160°C for reaction, cooling and removing the mixture after the reaction is completed; washing with deionized water and ethanol, filtering and washing with deionized water and ethanol three times each, collecting AHF-5 crystals, and drying in air to finally obtain crystalline AHF-5 powder; The molar ratio of sodium hydroxide to Zn(oAC)2·H2O, 5-amino-1H-tetrazolyl, and pyromellitic acid is 6:2:2:1; Step 2: Iron, Cobalt, and Nickel Trimetallic Doping Ferric chloride, cobalt acetate, and nickel acetate are mixed and added to ethanol to obtain a mixed solution; the mixed solution is stirred, and crystalline AHF-5 powder is added to the solution during the stirring process. After the crystalline AHF-5 powder is added, the solution is continuously stirred until the ethanol is completely evaporated and stirred to dryness, thereby obtaining an iron-cobalt-nickel trimetallic doped MOF composite material; Step 3: dissolving polyacrylonitrile powder in N,N-dimethylformamide to obtain a PAN solution; grinding an iron, cobalt, and nickel trimetallic MOF composite material into powder, adding the powder to the PAN solution and stirring (the mass of the trimetallic MOF composite material is 8% of the mass of the polyacrylonitrile); then ultrasonically dispersing the powder until the solution is uniform to obtain a trimetallic MOF / PAN spinning solution; and electrospinning the trimetallic MOF / PAN spinning solution to obtain a trimetallic MOF / PAN nanofiber membrane. Step 4: High temperature carbonization The obtained trimetallic MOF / PAN nanofiber membrane was placed in a porcelain boat under a nitrogen atmosphere and placed in a tube furnace for carbonization annealing at 800°C for 2 hours. Polyurethane was used as a binder, and the carbonized nanofiber membrane and polyurethane were mixed under vacuum drying to obtain a trimetallic MOF absorbing membrane. The mass ratio of polyurethane to the tri-metallic MOF / PAN nanofiber membrane before annealing in step 3 was 6:1. Example 5 Step 1, adding Zn(oAC)2·H2O, 5-amino-1H-tetrazole, and pyromellitic acid to deionized water, and pouring the mixture into a polytetrafluoroethylene-lined autoclave to form a mixed solution; stirring the mixed solution at room temperature, and simultaneously adding sodium hydroxide to adjust the pH value to 7; placing the mixture into a reactor, and placing the mixture in an oven at 170°C for heating to react, cooling and removing the mixture after the reaction is completed; washing with deionized water and ethanol, filtering and washing with deionized water and ethanol three times each, collecting AHF-5 crystals, and drying in air to finally obtain crystalline AHF-5 powder; The molar ratio of sodium hydroxide to Zn(oAC)2·H2O, 5-amino-1H-tetrazolyl, and pyromellitic acid is 6:2:2:1; Step 2: Iron, Cobalt, and Nickel Trimetallic Doping Ferric chloride, cobalt acetate, and nickel acetate are mixed and added to ethanol to obtain a mixed solution; the mixed solution is stirred, and crystalline AHF-5 powder is added to the solution during the stirring process. After the crystalline AHF-5 powder is added, the solution is continuously stirred until the ethanol is completely evaporated and stirred to dryness, thereby obtaining an iron-cobalt-nickel trimetallic doped MOF composite material; Step 3: dissolving polyacrylonitrile powder in N,N-dimethylformamide to obtain a PAN solution; grinding an iron, cobalt, and nickel trimetallic MOF composite material into powder, adding the powder to the PAN solution and stirring (the mass of the trimetallic MOF composite material is 10% of the mass of the polyacrylonitrile); then ultrasonically dispersing the powder until the solution is uniform to obtain a trimetallic MOF / PAN spinning solution; and electrospinning the trimetallic MOF / PAN spinning solution to obtain a trimetallic MOF / PAN nanofiber membrane. Step 4: High temperature carbonization The obtained trimetallic MOF / PAN nanofiber membrane was placed in a porcelain boat under a nitrogen atmosphere and placed in a tube furnace for carbonization annealing at 800°C for 2 hours. Polyurethane was used as a binder, and the carbonized nanofiber membrane and polyurethane were mixed under vacuum drying to obtain a trimetallic MOF absorbing membrane. The mass ratio of polyurethane to the tri-metallic MOF / PAN nanofiber membrane before annealing in step 3 was 6:1. Example 6 Step 1, adding Zn(oAC)2·H2O, 5-amino-1H-tetrazole, and pyromellitic acid to deionized water, and pouring the mixture into a polytetrafluoroethylene-lined autoclave to form a mixed solution; stirring the mixed solution at room temperature, and simultaneously adding sodium hydroxide to adjust the pH value to 6; placing the mixture into a reactor, and heating the mixture in an oven at 160°C for reaction, cooling and removing the mixture after the reaction is completed; washing with deionized water and ethanol, filtering and washing with deionized water and ethanol three times each, collecting AHF-5 crystals, and drying in air to finally obtain crystalline AHF-5 powder; The molar ratio of sodium hydroxide to Zn(oAC)2·H2O, 5-amino-1H-tetrazolyl, and pyromellitic acid is 6:2:2:1; Step 2: Iron, Cobalt, and Nickel Trimetallic Doping Ferric chloride, cobalt acetate, and nickel acetate are mixed and added to ethanol to obtain a mixed solution; the mixed solution is stirred, and crystalline AHF-5 powder is added to the solution during the stirring process. After the crystalline AHF-5 powder is added, the solution is continuously stirred until the ethanol is completely evaporated and stirred to dryness, thereby obtaining an iron-cobalt-nickel trimetallic doped MOF composite material; Step 3: dissolving polyacrylonitrile powder in N,N-dimethylformamide to obtain a PAN solution; grinding a trimetallic MOF composite material doped with iron, cobalt, and nickel into powder, adding the powder to the PAN solution and stirring (the mass of the trimetallic MOF composite material is 5% of the mass of the polyacrylonitrile); then ultrasonically dispersing the powder until the solution is uniform to obtain a trimetallic MOF / PAN spinning solution; and electrospinning the trimetallic MOF / PAN spinning solution to obtain a trimetallic MOF / PAN nanofiber membrane. Step 4: High temperature carbonization The obtained trimetallic MOF / PAN nanofiber membrane was placed in a porcelain boat under a nitrogen atmosphere and placed in a tube furnace for carbonization annealing at 800°C for 2 hours. Polyurethane was used as a binder, and the carbonized nanofiber membrane and polyurethane were mixed under vacuum drying to obtain a trimetallic MOF absorbing membrane. The mass ratio of polyurethane to the tri-metallic MOF / PAN nanofiber membrane before annealing in step 3 was 6:1. like Figure 2This is the XRD pattern of the AHF-5 crystal material in the present invention. By comparing it with the standard card, the crystal planes of Zn, N and C can be observed, and the stability before and after treatment is maintained.

[0030] like Figure 3 This graph shows the reflection loss (RL) of the magnetic trimetallic MOF (AHF-5) composite polyurethane absorbing film of the present invention at different thicknesses. It shows that at 2.4 mm, the reflection loss of the magnetic trimetallic MOF (AHF-5) composite polyurethane absorbing film prepared using electrospinning technology reaches -66.39 dB, demonstrating the material's excellent electromagnetic wave absorption properties.

[0031] like Figure 4 This is a graph showing the bandwidth of the magnetic trimetallic MOF (AHF-5) composite polyurethane absorbing film of the present invention. At 1.63 mm, the effective absorption bandwidth is 13.08 GHz to 18 GHz, essentially covering the entire Ku band. At 2.4 mm, the effective absorption bandwidth is 8.56 GHz to 11.28 GHz, essentially covering the entire X band.

[0032] like Figure 5 This is a plot of the real part of the dielectric loss of the magnetic trimetallic MOF (AHF-5) composite polyurethane absorbing film prepared in this invention. The real part of the dielectric constant (ε') decreases gradually over the entire 2 GHz to 8 GHz range.

[0033] like Figure 6 This plot shows the imaginary part of the dielectric loss of the magnetic trimetallic MOF (AHF-5) composite polyurethane absorbing film prepared in this invention. The imaginary part of the dielectric constant (ε") decreases between 2 GHz and 6 GHz and fluctuates around an imaginary part of 4 between 6 GHz and 18 GHz.

[0034] like Figure 7 This is the tangent graph of the dielectric loss of the magnetic trimetallic MOF (AHF-5) composite polyurethane absorbing film prepared by the present invention. The tangent value of the dielectric loss (Tanδ ε =ε" / ε') decreases slowly and then increases slowly within 2GHz~6GHz, but the value remains between 0.3 and 0.5.

[0035] like Figure 8 This plot shows the real part of the magnetic loss of the trimetallic MOF (AHF-5) composite polyurethane absorbing film prepared in this invention. The real part of the magnetic loss (μ') remains essentially stable at 1 over the entire frequency range of 2 GHz to 18 GHz.

[0036] like Figure 9 This graph shows the imaginary part of the magnetic loss of the trimetallic MOF (AHF-5) composite polyurethane absorbing film prepared in this invention. The imaginary part of the magnetic loss (μ") decreases oscillatingly over the entire frequency range from 2 GHz to 18 GHz.

[0037] like Figure 10 This is the tangent graph of the magnetic loss of the magnetic trimetallic MOF (AHF-5) composite polyurethane absorbing film prepared by the present invention. The tangent value of the magnetic loss (Tanδ μ =μ" / μ') decreases in an oscillatory manner from 2GHz to 18GHz, which is basically the same as the imaginary part curve of magnetic loss.

[0038] Combine Figures 1 to 10 It was found that in the electromagnetic wave absorption performance test, the reflection loss value of the material at 2.4mm reached -66.39dB when the electrospinning technology was used to prepare the magnetic tri-metallic MOF (AHF-5) composite polyurethane absorbing film. exist At 2.0 mm, the effective absorption bandwidth is 10.44 GHz to 14.16 GHz, covering parts of the Ku-band and X-band. At 1.63 mm, the effective absorption bandwidth is 13.08 GHz to 18 GHz, covering the vast majority of the Ku-band. This indicates that the prepared composite material has high microwave absorption performance. Furthermore, the real part of the magnetic permeability is essentially stable around 1, while the imaginary part of the magnetic permeability fluctuates around 0. The dielectric loss tangent and magnetic loss tangent also maintain a well-defined fluctuation trend, indicating that dielectric and magnetic losses play an important synergistic role in the microwave absorption process.

[0039] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to specific embodiments. Obviously, many modifications and variations are possible based on the contents of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a magnetic trimetallic MOF / AHF-5 composite polyurethane absorbing film, characterized in that: First, the metal-organic framework material is synthesized by the hydrothermal method, and a hybrid crystalline metal-organic framework containing three metals, iron, cobalt and nickel, is stirred and doped; by adjusting the ratio of iron, cobalt and nickel metals, the chemical composition of the polymer crystalline precursor is regulated. Through electrospinning technology, the magnetic trimetallic MOF is loaded into a uniformly grown nanofiber membrane, and then carbonized and mixed with polyurethane to obtain a trimetallic MOF absorbing membrane.

2. The method for preparing the magnetic trimetallic MOF / AHF-5 composite polyurethane absorbing film according to claim 1, wherein the specific steps are as follows: Step 1, adding Zn(oAC)2·H2O, 5-amino-1H-tetrazole, and pyromellitic acid to deionized water, and pouring the mixture into a polytetrafluoroethylene-lined autoclave to form a mixed solution; stirring the mixed solution at room temperature, and simultaneously adding sodium hydroxide to adjust the pH value to 6-7; placing the mixture into a reactor, and placing it in an oven for heating and reaction, cooling and removing the mixture after the reaction is completed; washing with deionized water and ethanol, filtering and collecting to obtain AHF-5 crystals, and drying in air to finally obtain crystalline AHF-5 powder; Step 2: Iron, Cobalt, and Nickel Trimetallic Doping Ferric chloride, cobalt acetate, and nickel acetate are mixed and added to ethanol to obtain a mixed solution; the mixed solution is stirred, and crystalline AHF-5 powder is added to the solution during the stirring process. After the crystalline AHF-5 powder is added, the solution is continuously stirred until the ethanol is completely evaporated and stirred to dryness, thereby obtaining an iron-cobalt-nickel trimetallic doped MOF composite material; Step 3: dissolving polyacrylonitrile powder in N,N-dimethylformamide to obtain a PAN solution; grinding the iron, cobalt, and nickel trimetallic MOF composite material into powder, adding the powder to the PAN solution and stirring, followed by ultrasonic dispersion until the solution is uniform to obtain a trimetallic MOF / PAN spinning solution; electrospinning the trimetallic MOF / PAN spinning solution to obtain a trimetallic MOF / PAN nanofiber membrane; Step 4: High temperature carbonization The obtained tri-metallic MOF / PAN nanofiber membrane was placed into a porcelain boat under a nitrogen atmosphere and placed in a tubular furnace for carbonization annealing. Polyurethane was selected as a binder, and the carbonized nanofiber membrane was mixed with polyurethane under vacuum drying to obtain a tri-metallic MOF absorbing membrane.

3. The method for preparing the magnetic trimetallic MOF / AHF-5 composite polyurethane absorbing film according to claim 2, characterized in that: The Zn(oAC)2·H2O in step 1 can be replaced by zinc acetate or zinc nitrate.

4. The method for preparing the magnetic trimetallic MOF / AHF-5 composite polyurethane absorbing film according to claim 2, characterized in that: In step 1, the molar ratio of sodium hydroxide to Zn(oAC)2·H2O, 5-amino-1H-tetrazolyl and pyromellitic acid is 6:2:2:

1.

5. The method for preparing the magnetic trimetallic MOF / AHF-5 composite polyurethane absorbing film according to claim 2, characterized in that: In step 1, the heating temperature is 160° C. to 170° C., and the reaction time is 36 h to 40 h.

6. The method for preparing the magnetic trimetallic MOF / AHF-5 composite polyurethane absorbing film according to claim 2, characterized in that: In step 1, the filtration was performed by suction filtration, and the product was washed three times with deionized water and ethanol respectively.

7. The method for preparing the magnetic trimetallic MOF / AHF-5 composite polyurethane absorbing film according to claim 2, characterized in that: The ferric chloride, cobalt acetate and nickel acetate in step 2 can be replaced by corresponding iron, cobalt and nickel salts, and the mass ratio of single metal iron, cobalt and nickel in the ferric chloride, cobalt acetate and nickel acetate is 1:1:

1.

8. The method for preparing the magnetic trimetallic MOF / AHF-5 composite polyurethane absorbing film according to claim 2, characterized in that: The mass of the tri-metal doped MOF composite material in step 3 is 5%-10% of the mass of the polyacrylonitrile.

9. The method for preparing the magnetic trimetallic MOF / AHF-5 composite polyurethane absorbing film according to claim 2, characterized in that: In step 4, the annealing temperature is 800° C. and the annealing time is 2 hours.

10. The method for preparing the magnetic trimetallic MOF / AHF-5 composite polyurethane absorbing film according to claim 2, characterized in that: The mass ratio of the polyurethane in step 4 to the tri-metallic MOF / PAN nanofiber membrane before annealing in step 3 is 6:1.

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