A kind of string bead shape cobalt-doped Bi 25 FeO 40 Preparation method of / BiFeO3 nanofiber wave-absorbing material

Abstract

This invention discloses a beaded cobalt-doped Bi 25 FeO 40 The preparation method of / BiFeO3 nanofiber microwave absorbing material involves obtaining a precursor through a static method, then adding it together with bismuth nitrate, ferric nitrate, and a spinning aid into a mixed solvent composed of N,N-dimethylformamide and anhydrous ethanol to obtain a spinning solution. The spinning solution is then spun using electrospinning technology to obtain a nanofiber membrane. Finally, the material is obtained after drying and calcination. This microwave absorbing material increases the multiple reflections and scattering of electromagnetic waves, improving electromagnetic wave absorption performance. Furthermore, the heterogeneous interface formed after the two-phase composite further increases the interfacial polarization loss, resulting in a minimum reflection loss of -56.01 dB at a thickness of 2.33 mm and an effective absorption bandwidth of 6.32 GHz, covering the entire Ku-band.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic absorption materials technology, and relates to a beaded cobalt-doped Bi material. 25 FeO 40 Preparation method of / BiFeO3 nanofiber microwave absorbing material. Background Technology

[0002] Over the past few decades, electromagnetic technology has developed rapidly. While electromagnetic waves have brought convenience to fields such as healthcare, transportation, wireless communication, and national defense due to their advantages in wireless, long-distance, and high-speed transmission, electromagnetic pollution has also become increasingly serious. Excessive electromagnetic radiation and interference pose potential threats to electronic instruments and the human body. Therefore, there is an urgent need to develop high-performance electromagnetic wave absorbing materials.

[0003] Bismuth ferrite (BiFeO3) is the most widely studied multiferroic material, exhibiting strong ferroelectric and magnetic ordering at room temperature. Its low cost, abundant Earth resources, and non-toxicity make it an excellent electromagnetic wave absorber. However, pure-phase BiFeO3 suffers from poor absorption performance due to its single loss mechanism and significant leakage current, which significantly weakens the attenuation effect of dielectric loss on electromagnetic waves. Furthermore, the generation of oxygen vacancies in the crystal structure leads to magnetic instability, further reducing magnetic loss efficiency. Currently explored modified BiFeO3 materials suffer from problems such as unremarkable microstructure and relatively low electromagnetic wave absorption performance. Specifically, modified materials are mostly irregular blocks or aggregated particles, lacking a controllable multi-level microstructure, resulting in short electromagnetic wave reflection and scattering paths. In some modified systems, poor interfacial compatibility between heterogeneous phases easily forms charge accumulation dead zones, which suppress interfacial polarization loss. Moreover, most modified materials have narrow absorption bandwidths, achieving effective absorption only in specific frequency bands, making it difficult to cover the complex electromagnetic frequency bands in practical applications.

[0004] Based on this, the present invention introduces abundant heterogeneous interfaces through electrospinning, and attenuates electromagnetic wave energy through interface polarization loss; at the same time, the one-dimensional structure of the composite material provides a high specific surface area, increases the number of reflections and scatterings of incident electromagnetic waves, increases its energy consumption, and thus improves electromagnetic wave absorption performance. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide a beaded cobalt-doped Bi 25 FeO 40The preparation method of / BiFeO3 nanofiber microwave absorbing material involves obtaining a precursor through a static method, then adding it together with bismuth nitrate, ferric nitrate, and a spinning aid into a mixed solvent composed of N,N-dimethylformamide and anhydrous ethanol to obtain a spinning solution. The spinning solution is then spun using electrospinning technology to obtain a nanofiber membrane. Finally, the material is obtained after drying and calcination. This microwave absorbing material increases the multiple reflections and scattering of electromagnetic waves, improving electromagnetic wave absorption performance. Furthermore, the heterogeneous interface formed after the two-phase composite further increases the interfacial polarization loss, resulting in a minimum reflection loss of -56.01 dB at a thickness of 2.33 mm and an effective absorption bandwidth of 6.32 GHz, covering the entire Ku-band.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A beaded cobalt-doped Bi 25 FeO 40 The preparation method of BiFeO3 nanofiber microwave absorbing material is carried out in the following order:

[0008] (1) Dissolve 0.29 g of cobalt nitrate in 35 mL of deionized water to obtain solution A. Dissolve 0.33 g of 2-methylimidazole in 35 mL of deionized water to obtain solution B. Quickly pour solution A into solution B, stir evenly, and let stand for 12-24 h to obtain a purple precipitate. After centrifugation and washing, the purple precipitate is dried at 40-70 ℃ for 2-6 h to obtain the precursor.

[0009] (2) Dissolve bismuth nitrate and ferric nitrate in a mixed solvent, then add the precursor and spinning aid to it, and stir at a stirring rate of 150-450 rpm for 8-14 h to obtain a spinning solution;

[0010] (3) Electrospinning the spinning solution to obtain nanofiber membranes;

[0011] (4) After vacuum drying and calcination of the nanofiber membrane, beaded cobalt-doped Bi was obtained. 25 FeO 40 / BiFeO3 nanofiber microwave absorbing material.

[0012] As a limitation of the present invention, in step (2), the mixed solvent is composed of N,N-dimethylformamide and anhydrous ethanol, and the mass ratio of N,N-dimethylformamide to anhydrous ethanol is 9.445:7.89.

[0013] As another limitation of the present invention, in step (2), the spinning aid is polyvinylpyrrolidone or polyacrylonitrile.

[0014] As a third limitation of the present invention, in step (2), the mass ratio of bismuth nitrate to ferric nitrate, mixed solvent, precursor and spinning aid is 1.0034:(0.747-0.788):17.335:(0.05-0.15):2.

[0015] In this invention, the mass ratio of bismuth nitrate to ferric nitrate, mixed solvent, precursor, and spinning aid affects the spinning effect of the precursor solution and the fiber morphology. When the mass ratio is within this range, the spinning process is relatively stable, and the proportion of metal salts during sintering is appropriate, which is conducive to the stable formation of fibers. When the mass ratio is less than this range, the content of metal salts is too low, which leads to the collapse of fiber morphology. When the mass ratio is greater than this range, the content of metal salts is too high, which leads to uneven fiber output during the spinning process and makes continuous spinning difficult.

[0016] As a fourth limitation of the present invention, in step (3), the injection speed during electrospinning is 0.05-0.2 mm / min, the needle diameter is 20-25 G, the distance between the nozzle and the rotating roller is 15-25 cm, the receiving speed of the rotating roller is 20-60 r / min, the positive spinning voltage is 12-18 kV, the negative voltage is 0.5-3 kV, the temperature is 20-30 ℃, and the humidity is 15-30%.

[0017] As a fifth limitation of the present invention, in step (4), the drying temperature is 60-80 °C, the time is 8-12 h, and the vacuum degree is 0.06 MPa.

[0018] As a sixth limitation of the present invention, in step (4), the calcination process is carried out in the following order:

[0019] (a) In the first heating stage, the temperature is increased from room temperature to 300 ℃ at a heating rate of 1-5 ℃ / min, and held for 1-3 h;

[0020] (b) In the second heating stage, the temperature is increased from 300℃ to 550℃ at a heating rate of 1-5℃ / min, and held for 1-3 hours;

[0021] (c) During the cooling phase, the temperature is reduced to room temperature at a rate of 1-5 °C / min.

[0022] In this invention, the calcination stage affects the morphology of the nanofibers. In the first heating stage, when the temperature is increased from room temperature to 300℃ at a rate of 1-5℃ / min, the spinning aid begins to decompose slowly. Holding this temperature for 1-3 hours facilitates the complete decomposition of organic matter, preventing residual organic matter from interfering with subsequent crystallization, and allowing the metal salt to form oxide precursors. In the second heating stage, when the calcination temperature is increased from 300℃ to 550℃ at a rate of 1-5℃ / min, the metal salt further thermally decomposes, generating oxide nuclei. In the interwoven regions of the fiber network, the metal salt precursors are enriched due to electrospinning capillary action, providing high-concentration sites for heterogeneous nucleation. The nucleation rate is significantly higher than in the main fiber region, preferentially growing into microparticle aggregates, forming an initial beaded structure. As the temperature increases, the atomic diffusion rate significantly increases, the nuclei gradually grow, and the bead size increases. Holding this temperature for 1-3 hours facilitates the full growth of the beads, ensuring size uniformity. During cooling, a cooling rate of 1-5℃ / min is used to maintain a uniform beaded morphology and prevent morphological distortion caused by excessively rapid cooling.

[0023] The beaded structure increases the specific surface area of ​​the fiber, enhancing multiple reflections and scattering of electromagnetic waves and improving its electromagnetic wave absorption capability. Meanwhile, Bi... 25 FeO 40 Atomic interdiffusion occurs at the interface with BiFeO3, forming a gradient interface that can enhance the bonding force between the beads and the fibers.

[0024] The above-mentioned technical solution of the present invention is a whole in which each step is closely related and mutually influential, and together they determine the morphological characteristics and performance of the product.

[0025] The above technical solution has the following advantages or beneficial effects:

[0026] 1. This invention prepares cobalt-doped Bi based on the static settling method, sol-gel method, and electrospinning process. 25 FeO 40 / BiFeO3 nanofibers exhibit a one-dimensional beaded morphology, characterized by thinness, wide frequency range, and strong absorption, and possess excellent wave absorption properties.

[0027] 2. This invention constructs Bi by introducing cobalt. 25 FeO 40 The heterostructure with BiFeO3 improves the interfacial polarization loss, increases the attenuation of electromagnetic waves, and improves impedance matching. At the same time, the presence of the beaded structure increases the specific surface area of ​​the fiber, increases the multiple reflections and scattering of electromagnetic waves, and enhances the electromagnetic wave absorption capability.

[0028] 3. The cobalt-doped Bi prepared by this invention 25 FeO40 / BiFeO3 nanofibers with a thickness of 2.33 mm achieve a minimum reflection loss of -56.01 dB and an effective absorption bandwidth of 6.32 GHz;

[0029] 4. The preparation process of this invention is simple and the cost is low, making it suitable for large-scale industrial production.

[0030] This invention is applicable to the preparation of beaded cobalt-doped Bi 25 FeO 40 / BiFeO3 nanofiber microwave absorbing material.

[0031] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0032] Figure 1 The beaded cobalt-doped Bi prepared in Examples 1-3 of this invention 25 FeO 40 XRD pattern of BiFeO3 nanofiber microwave absorbing material;

[0033] Figure 2 The beaded cobalt-doped Bi prepared in Examples 1-3 of this invention 25 FeO 40 SEM images of BiFeO3 nanofiber microwave absorbing materials, wherein: (a) is the SEM image of Example 1, (b) is the SEM image of Example 2, and (c) is the SEM image of Example 3;

[0034] Figure 3 The beaded cobalt-doped Bi prepared in Example 3 of this invention 25 FeO 40 EDS spectra of / BiFeO3 nanofiber microwave absorbing material, where: (a) is the elemental distribution of Bi, (b) is the elemental distribution of Fe, (c) is the elemental distribution of O, and (d) is the elemental distribution of Co;

[0035] Figure 4 The beaded cobalt-doped Bi prepared in Example 1 of this invention 25 FeO 40 / Reflection loss diagram of BiFeO3 nanofiber absorbing material combined with paraffin;

[0036] Figure 5 The beaded cobalt-doped Bi prepared in Example 2 of this invention 25 FeO 40 / Reflection loss diagram of BiFeO3 nanofiber absorbing material combined with paraffin;

[0037] Figure 6The beaded cobalt-doped Bi prepared in Example 3 of this invention 25 FeO 40 / Reflection loss diagram of BiFeO3 nanofiber absorbing material combined with paraffin wax. Detailed Implementation

[0038] The following embodiments are merely some, not all, of the embodiments of the present invention. Therefore, the detailed descriptions of the embodiments provided below are not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0039] In this invention, unless otherwise specified, all equipment and raw materials are commercially available or commonly used in the industry. The methods described in the following embodiments are conventional methods in the art, unless otherwise specified. Example 1

[0040] This embodiment prepares a beaded cobalt-doped Bi 25 FeO 40 The preparation process and steps of the / BiFeO3 nanofiber microwave absorbing material are as follows:

[0041] (1) Dissolve 0.29 g of cobalt nitrate in 35 mL of deionized water to obtain solution A. Dissolve 0.33 g of 2-methylimidazole in 35 mL of deionized water to obtain solution B. Quickly pour solution A into solution B, stir evenly, and let stand for 24 h to obtain a purple precipitate. After centrifugation and washing, the purple precipitate is dried at 40 ℃ for 6 h to obtain the precursor.

[0042] (2) Dissolve 1.0034 g of bismuth nitrate and 0.788 g of ferric nitrate in 17.335 g of mixed solvent (the mixed solvent is composed of 9.445 g of N,N-dimethylformamide and 7.89 g of anhydrous ethanol), stir until clear and transparent, add 0.05 g of precursor, stir evenly, then add 2 g of polyvinylpyrrolidone, stir at a stirring rate of 150 rpm for 8 h to obtain spinning solution;

[0043] (3) The above spinning solution was electrospun, with the following settings: injection speed of 0.05 mm / min, needle diameter of 22G, distance between nozzle and roller of 15 cm, receiving speed of roller of 30 r / min, positive spinning voltage of 12 kV, negative voltage of 0.5 kV, temperature of 20 ℃, and humidity of 15%, to obtain nanofiber membrane;

[0044] (4) The nanofiber membrane was placed in a vacuum drying oven and dried for 10 h at a vacuum of 0.06 MPa and a temperature of 70 °C. After being removed, it was placed in a muffle furnace and heated from room temperature to 300 °C at a heating rate of 5 °C / min and held for 1 h. Then, it was heated from 300 °C to 550 °C at a heating rate of 5 °C / min and held for 1 h. Finally, it was cooled to room temperature at a cooling rate of 5 °C / min to obtain beaded cobalt-doped Bi. 25 FeO 40 / BiFeO3 nanofiber microwave absorbing material. Example 2

[0045] This embodiment prepares a beaded cobalt-doped Bi 25 FeO 40 The preparation process and steps of the / BiFeO3 nanofiber microwave absorbing material are as follows:

[0046] (1) Dissolve 0.29 g of cobalt nitrate in 35 mL of deionized water to obtain solution A. Dissolve 0.33 g of 2-methylimidazole in 35 mL of deionized water to obtain solution B. Quickly pour solution A into solution B, stir evenly, and let stand for 20 h to obtain a purple precipitate. After centrifugation and washing, the purple precipitate is dried at 60 ℃ for 4 h to obtain the precursor.

[0047] (2) Dissolve 1.0034 g of bismuth nitrate and 0.768 g of ferric nitrate in 17.335 g of mixed solvent (the mixed solvent is composed of 9.445 g of N,N-dimethylformamide and 7.89 g of anhydrous ethanol), stir until clear and transparent, add 0.1 g of precursor, stir evenly, then add 2 g of polyvinylpyrrolidone, stir at 300 rpm for 14 h to obtain spinning solution;

[0048] (3) The above spinning solution was electrospun, with the following settings: injection speed of 0.15 mm / min, needle diameter of 20G, distance between nozzle and roller of 20 cm, receiving speed of roller of 20 r / min, positive spinning voltage of 15 kV, negative voltage of 2 kV, temperature of 25 ℃, and humidity of 25%, to obtain nanofiber membrane;

[0049] (4) The nanofiber membrane was placed in a vacuum drying oven and dried at a vacuum of 0.06 MPa and a temperature of 60℃ for 12 h. After being removed, it was placed in a muffle furnace and heated from room temperature to 300℃ at a heating rate of 3℃ / min, and held at that temperature for 2 h. Then, it was heated from 300℃ to 550℃ at a heating rate of 3℃ / min, and held at that temperature for 2 h. Finally, it was cooled to room temperature at a cooling rate of 3℃ / min to obtain beaded cobalt-doped Bi. 25 FeO 40 / BiFeO3 nanofiber microwave absorbing material. Example 3

[0050] This embodiment prepares a beaded cobalt-doped Bi 25 FeO 40 The preparation process and steps of the / BiFeO3 nanofiber microwave absorbing material are as follows:

[0051] (1) Dissolve 0.29 g of cobalt nitrate in 35 mL of deionized water to obtain solution A. Dissolve 0.33 g of 2-methylimidazole in 35 mL of deionized water to obtain solution B. Quickly pour solution A into solution B, stir evenly, and let stand for 12 h to obtain a purple precipitate. After centrifugation and washing, the purple precipitate is dried at 70℃ for 2 h to obtain the precursor.

[0052] (2) Dissolve 1.0034 g of bismuth nitrate and 0.747 g of ferric nitrate in 17.335 g of mixed solvent (the mixed solvent is composed of 9.445 g of N,N-dimethylformamide and 7.89 g of anhydrous ethanol), stir until clear and transparent, add 0.15 g of precursor, stir evenly, then add 2 g of polyvinylpyrrolidone, stir at a stirring rate of 450 rpm for 10 h to obtain spinning solution;

[0053] (3) Electrospinning the above spinning solution, setting the injection speed to 0.2 mm / min, the needle diameter to 25G, the distance between the nozzle and the rotating roller to 25 cm, the receiving speed of the rotating roller to 60 r / min, the positive spinning voltage to 18 kV, the negative voltage to 3 kV, the temperature to 30℃, and the humidity to 30%, to obtain a nanofiber membrane.

[0054] (4) The nanofiber membrane was placed in a vacuum drying oven and dried for 8 h at a vacuum of 0.06 MPa and a temperature of 80 °C. After being removed, it was placed in a muffle furnace and heated from room temperature to 300 °C at a heating rate of 1 °C / min and held for 3 h. Then, it was heated from 300 °C to 550 °C at a heating rate of 1 °C / min and held for 3 h. Finally, it was cooled to room temperature at a cooling rate of 1 °C / min to obtain beaded cobalt-doped Bi. 25 FeO 40 / BiFeO3 nanofiber microwave absorbing material. Comparative Example

[0055] To investigate the influence of different parameters or preparation methods on the performance of the product of this invention, the following comparative experiments were conducted. Different microwave absorbing materials were prepared in the following comparative examples:

[0056] Comparative Example 1

[0057] This comparative example prepares a microwave absorbing material. The preparation process is similar to that of Example 1. The only difference is that in the calcination process of step (4), instead of segmented calcination, the temperature is directly raised from room temperature to 550°C at a heating rate of 5°C / min, held for 2 hours, and then cooled to room temperature at a cooling rate of 5°C / min.

[0058] Comparative Example 2

[0059] This comparative example prepares a BiFeO3 microwave absorbing material. The preparation process and steps are as follows:

[0060] 1.0034 g of bismuth nitrate and 0.747 g of ferric nitrate were dissolved in 9.445 g of N,N-dimethylformamide and 7.89 g of anhydrous ethanol. After stirring until clear and transparent, 2 g of polyvinylpyrrolidone was added, and the mixture was stirred at 450 rpm for 12 h to obtain the spinning solution.

[0061] Electrospinning was performed on the spinning solution with the following settings: injection speed of 0.2 mm / min, needle diameter of 22 G, distance between nozzle and roller of 15 cm, receiving speed of roller of 30 r / min, positive spinning voltage of 15 kV, negative spinning voltage of 2 kV, temperature of 20℃, and humidity of 15% to obtain nanofiber membrane.

[0062] The nanofiber membrane was placed in a vacuum drying oven and dried at a vacuum of 0.06 MPa and a temperature of 70 ℃ for 10 h.

[0063] The dried nanofiber membrane was placed in a muffle furnace and heated from room temperature to 550°C at a heating rate of 1°C / min, held at that temperature for 3 h, and then cooled to room temperature at a cooling rate of 1°C / min to obtain BiFeO3 nanofibers.

[0064] Comparative Example 3

[0065] This comparative example prepares a microwave absorbing material. The preparation process is similar to that of Example 1, except that in step (1), cobalt nitrate is replaced with nickel nitrate. The remaining steps and parameters are the same as those in Example 1.

[0066] Performance testing

[0067] The microwave absorbing materials prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to a series of morphology and performance tests. The specific test results are as follows:

[0068] Figure 1 The beaded cobalt-doped Bi prepared in Examples 1-3 of this invention 25 FeO 40 The XRD pattern of the / BiFeO3 nanofiber absorbing material shows that the present invention has successfully prepared beaded cobalt-doped Bi25 FeO 40 / BiFeO3 nanofibers exhibit good crystallinity.

[0069] Figure 2 The beaded cobalt-doped Bi prepared in Examples 1-3 of this invention 25 FeO 40 SEM image of the / BiFeO3 nanofiber absorbing material, showing the beaded cobalt-doped Bi2O3 nanofiber material prepared in Example 1 in (a). 25 FeO 40 The / BiFeO3 nanofiber absorbing material exhibits a relatively uniform fibrous structure, at which point a beaded structure has already formed; as observed in (b) and (c), with the continuous increase of the amount of cobalt precursor added, the beaded structure shows a clear trend of increasing size and denser distribution.

[0070] Figure 3 The beaded cobalt-doped Bi prepared in Example 3 of this invention 25 FeO 40 The EDS spectrum of the / BiFeO3 nanofiber absorbing material shows that Bi, Fe, O, and Co elements are uniformly distributed inside the material.

[0071] 0.084 g of the nanofiber absorbing material prepared in Examples 1-3 and Comparative Examples 1-3 and 0.036 g of paraffin were weighed respectively, mixed with petroleum ether, pressed into concentric rings, and their electromagnetic parameters in the range of 2-18 GHz were tested using a vector network analyzer. Figures 4-6 The beaded cobalt-doped Bi prepared in Examples 1-3 of this invention 25 FeO 40 The reflection loss diagram of the / BiFeO3 nanofiber absorbing material shows that the cobalt-doped Bi2O3 prepared in Example 3 has a lower reflection loss than the material itself. 25 FeO 40 The / BiFeO3 nanofiber absorbing material exhibits the best absorption performance. This material possesses abundant heterogeneous interfaces, which can increase interfacial polarization loss. Furthermore, due to its unique beaded structure, it can increase multiple reflections and scattering of electromagnetic waves, thereby achieving a minimum reflection loss of -56.01 dB and an effective absorption bandwidth of 6.32 GHz with a thickness of 2.33 mm.

[0072] The table below shows the minimum reflection loss and effective absorption bandwidth of the absorbing materials prepared in Comparative Examples 1-3 at a thickness of 2.33 mm. The specific values ​​are as follows:

[0073] ,

[0074] From the above table and Figures 4-6It can be seen that, compared with Comparative Examples 1-3, the Bi prepared in Examples 1-3... 25 FeO 40 The absorption performance of the BiFeO3 nanofiber absorbing material was significantly improved, and the bandwidth was increased. This is because segmented heating better maintains the formation of the beaded morphology, the addition of cobalt nitrate introduces a heterogeneous interface, increasing interfacial polarization, and the introduction of magnetic metal also improves impedance matching. Comparative Example 1, due to its one-step heating method, caused the fiber structure to collapse, resulting in a decrease in its absorption performance. The BiFeO3 absorbing material prepared in Comparative Example 2 exhibited decreased absorption performance due to its singular polarization mechanism. Comparative Example 3, due to the use of nickel nitrate, had weaker magnetic properties than cobalt and lacked good impedance matching, thus leading to a decrease in its absorption performance.

[0075] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A string of beads of cobalt-doped Bi 25 FeO 40 / BiFeO3 nanofiber wave-absorbing material, characterized by, The following steps are carried out in sequence: (1) 0.29 g of cobalt nitrate is dissolved in 35 mL of deionized water to obtain solution A, and 0.33 g of 2-methylimidazole is dissolved in 35 mL of deionized water to obtain solution B. Solution A is quickly poured into solution B, and after stirring, the mixture is left to stand for 12-24 h to obtain a purple precipitate. The purple precipitate is washed by centrifugation and dried at 40-70 ℃ for 2-6 h to obtain a precursor; (2) bismuth nitrate and iron nitrate are dissolved in a mixed solvent, and the precursor and a spinning aid are added to the mixed solvent. The mass ratio of the bismuth nitrate, the iron nitrate, the mixed solvent, the precursor, and the spinning aid is 1.0034: (0.747-0.788): 17.335: (0.05-0.15):

2. The mixture is stirred at a stirring rate of 150-450 rpm for 8-14 h to obtain a spinning solution; (3) The spinning solution is electrospun to obtain a nanofiber membrane; (4) After vacuum drying and calcining the nanofiber membrane, a string-shaped cobalt-doped Bi 25 FeO 40 / BiFeO3 nanofiber wave-absorbing material; The calcination process is carried out in the following steps in sequence: (a) The first temperature rising stage: the temperature is raised from room temperature to 300 ℃ at a temperature rising rate of 1-5 ℃ / min, and the temperature is kept at 300 ℃ for 1-3 h; (b) The second temperature rising stage: the temperature is raised from 300 ℃ to 550 ℃ at a temperature rising rate of 1-5 ℃ / min, and the temperature is kept at 550 ℃ for 1-3 h; (c) The temperature lowering stage: the temperature is lowered to room temperature at a temperature lowering rate of 1-5 ℃ / min.

2. The one kind of string bead shape cobalt doped Bi 25 FeO 40 Preparation method of the string bead shape cobalt doped Bi In step (2), the mixed solvent is composed of N,N-dimethylformamide and anhydrous ethanol, and the mass ratio of N,N-dimethylformamide to anhydrous ethanol is 9.445: 7.

89.

3. The one kind of string bead shape cobalt doped Bi 25 FeO 40 Preparation method of the string bead shape cobalt doped Bi In step (2), the spinning aid is polyvinylpyrrolidone or polyacrylonitrile.

4. A beaded cobalt-doped Bi according to claim 1 25 FeO 40 The method for preparing BiFeO3 nanofiber microwave absorbing material is characterized by... In step (3), the injection speed during electrospinning is 0.05-0.2 mm / min, the needle aperture is 20-25 G, the distance between the nozzle and the rotating roller is 15-25 cm, the receiving speed of the rotating roller is 20-60 r / min, the positive voltage is 12-18 kV, the negative voltage is 0.5-3 kV, the temperature is 20-30 ℃, and the humidity is 15-30%.

5. A beaded cobalt-doped Bi according to claim 1 25 FeO 40 The method for preparing BiFeO3 nanofiber microwave absorbing material is characterized by... In step (4), the drying temperature is 60-80 ℃, the time is 8-12 h, and the vacuum degree is 0.06 MPa.

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