Preparation method of beaded cobalt-doped Bi25FeO40 / BiFeO3 nanofiber wave-absorbing material

Abstract

The invention discloses a preparation method of a beaded cobalt-doped Bi25FeO40 / BiFeO3 nanofiber wave-absorbing material, which comprises the following steps: obtaining a precursor by a standing method, and adding the precursor, bismuth nitrate, ferric nitrate and a spinning aid into a mixed solvent compounded by N, N-dimethylformamide and absolute ethyl alcohol to obtain a spinning solution; spinning the spinning solution by adopting an electrostatic spinning technology to obtain a nanofiber membrane; and finally, drying and calcining to obtain the wave-absorbing material. According to the wave-absorbing material, multiple reflection and scattering of electromagnetic waves are increased, the absorption performance of the electromagnetic waves is improved, due to the fact that a heterogeneous interface is generated after two phases are compounded, the interface polarization loss is further increased, when the thickness of the wave-absorbing material is 2.33 mm, the minimum reflection loss reaches-56.01 dB, the effective absorption frequency band width is 6.32 GHz, and the whole Ku wave band is covered.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electromagnetic absorbing materials, and relates to a preparation method of a string-bead-shaped cobalt-doped Bi 25 FeO 40 / BiFeO3 nanofiber wave-absorbing material. BACKGROUND

[0002] In the past few decades, electromagnetic technology has developed rapidly. Due to the advantages of electromagnetic waves in wireless, long-distance and high-speed transmission, it brings convenience in the fields of medical care, transportation, wireless communication, national defense security and the like, while electromagnetic pollution is also increasingly serious. Excessive electromagnetic radiation and interference are potential threats to electronic instruments and human bodies. Therefore, it is urgent to develop electromagnetic wave absorbing materials with excellent performance.

[0003] Bismuth ferrite (BiFeO3) is the most widely studied multiferroic material, which has strong ferroelectric and magnetic order at room temperature, and is an excellent electromagnetic wave absorbing material due to its low cost, rich earth resources and non-toxicity. However, pure-phase BiFeO3 has poor absorption performance due to a single loss mechanism, and it has a significant leakage current problem, which can significantly weaken the attenuation effect of dielectric loss on electromagnetic waves, and the magnetic order is unstable due to the generation of oxygen vacancies in the crystal structure, further reducing the magnetic loss efficiency. The materials explored for modification of BiFeO3 have problems such as unremarkable microstructure and small electromagnetic wave absorption performance. Specifically, the modified materials are mostly irregular blocks or agglomerated particles, lack of controllable multi-level microstructure, resulting in shorter electromagnetic wave reflection and scattering paths; and the interface compatibility between the heterogeneous phases in some modification systems is poor, which easily forms a charge accumulation dead angle, thereby inhibiting the interface polarization loss; in addition, the absorption frequency band width of most modified materials is narrow, and only effective absorption can be achieved in a specific frequency band, which is difficult to cover the complex electromagnetic frequency bands in actual applications.

[0004] Therefore, the application introduces rich heterogeneous interfaces by electrospinning, 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 reflection and scattering times of incident electromagnetic waves, increases the energy consumption, and thus improves the electromagnetic wave absorption performance. SUMMARY

[0005] In view of the above technical problems, the application aims to provide a string-bead-shaped cobalt-doped Bi 25 FeO 40The application discloses a preparation method of a string-bead-shaped cobalt-doped BiFeO3 nanofiber wave-absorbing material.

[0006] To achieve the above object, the technical scheme adopted by the application is as follows: A string-bead-shaped cobalt-doped Bi 25 FeO 40 The preparation method of the string-bead-shaped cobalt-doped BiFeO3 nanofiber wave-absorbing material is performed according to the following steps in sequence: (1) 0.29 g of cobalt nitrate is dissolved in 35 mL of deionized water to obtain solution A, 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 being uniformly stirred, the mixture is left to stand for 12-24 h to obtain a purple precipitate; the purple precipitate is centrifuged and washed, and then 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 then the precursor and a spinning aid are added thereto, and the mixture is stirred at a stirring speed 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-bead-shaped cobalt-doped Bi 25 FeO 40 / nanofiber wave-absorbing material is obtained.

[0007] As a limitation of the application, in step (2), the mixed solvent is compounded by N, N-dimethylformamide and anhydrous ethanol, and the mass ratio of N, N-dimethylformamide to anhydrous ethanol is 9.445:7.89.

[0008] As another limitation of the application, in step (2), the spinning aid is polyvinylpyrrolidone or polyacrylonitrile.

[0009] As the third limitation of the present application, in step (2), the mass ratio between the bismuth nitrate, the ferric nitrate, the mixed solvent, the precursor, and the spinning aid is 1.0034: (0.747-0.788): 17.335: (0.05-0.15): 2.

[0010] In the present application, the mass ratio between the bismuth nitrate, the ferric nitrate, the mixed solvent, the precursor, and the spinning aid affects the spinning effect of the precursor solution and the fiber morphology. When the mass ratio is as above, the spinning process is stable, the proportion of metal salts in the sintering process is appropriate, and the fiber is stable and formed. When the mass ratio is less than the above, the content of metal salts is too low, which leads to the collapse of the fiber morphology. When the mass ratio is greater than the above, the content of metal salts is too high, which leads to uneven fiber extrusion in the spinning process and makes it difficult to continuously spin.

[0011] As the fourth limitation of the present application, in step (3), the push injection speed during electrospinning is 0.05-0.2 mm / min, the needle hole 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 voltage for spinning is 12-18 kV, the negative voltage is 0.5-3 kV, the temperature is 20-30 ℃, and the humidity is 15-30%.

[0012] As the fifth limitation of the present application, in step (4), the drying temperature is 60-80 ℃, the time is 8-12 h, and the vacuum degree is 0.06 MPa.

[0013] As the sixth limitation of the present application, in step (4), the calcination process is performed in the following order: (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 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 for 1-3 h; (c) The temperature decreasing stage, the temperature is decreased to room temperature at a temperature decreasing rate of 1-5 ℃ / min.

[0014] In the present application, the calcination stage will affect the morphology of the nanofiber. In the first temperature rising stage, when the temperature is raised from room temperature to 300 DEG C at a temperature rising rate of 1-5 DEG C / min, the spinning aid will begin to decompose slowly; the temperature is kept for 1-3 h, which is beneficial to the complete decomposition of the organic matter, avoids the interference of the residual organic matter on the subsequent crystallization, and generates the oxide precursor of the metal salt. In the second temperature rising stage, when the calcination temperature is raised from 300 DEG C to 550 DEG C at a temperature rising rate of 1-5 DEG C / min, the metal salt is further thermally decomposed to generate the oxide nucleus; in the fiber cross network interlaced area, the metal salt precursor is enriched due to the capillary effect of electrospinning, which provides a high concentration site for heterogeneous nucleation; the nucleation rate of the crystal nucleus is significantly higher than that of the fiber main body area, and the crystal nucleus grows preferentially into a small particle aggregate to form an initial bead-like structure; as the temperature rises, the atomic diffusion rate is significantly improved, and the bead size increases; the temperature is kept for 1-3 h, which is beneficial to the complete growth of the bead and ensures the size uniformity. When the temperature is lowered, the temperature lowering rate is 1-5 DEG C / min, so as to maintain the uniform bead-like morphology and prevent the morphology from being distorted due to the too fast temperature lowering rate.

[0015] The existence of the bead-like structure increases the specific surface area of the fiber, increases the multiple reflection and scattering of the electromagnetic wave, and improves the electromagnetic wave absorption capacity. Meanwhile, the Bi 25 FeO 40 Atomic interdiffusion occurs at the interface of Bi

[0016] The above technical solutions of the present application are closely related and interact with each other as a whole, which jointly determines the morphology characteristics and performance of the product.

[0017] The above technical solutions have the following advantages or beneficial effects: 1. The present application is based on the static method, sol-gel method and electrospinning process, and the prepared cobalt-doped Bi 25 FeO 40 / BiFeO3 nanofiber presents a one-dimensional bead-like morphology, has a thin thickness, a wide frequency and a strong absorption, and has good wave absorption performance; 2. The present application introduces cobalt elements to construct the heterogeneous interface of Bi 25 FeO 40 and BiFeO3, improves the interface polarization loss, increases the attenuation of the electromagnetic wave, and improves the impedance matching; meanwhile, the existence of the bead-like structure increases the specific surface area of the fiber, increases the multiple reflection and scattering of the electromagnetic wave, and improves the electromagnetic wave absorption capacity; 3. The prepared cobalt-doped Bi 25 FeO 40The minimum reflection loss of the / BiFeO3 nanofiber is-56.01 dB when the thickness is 2.33 mm, and the effective absorption band width is 6.32 GHz; 4、The preparation process is simple, the cost is low, and the method is suitable for industrial large-scale production.

[0018] The application is suitable for preparing string-bead-shaped cobalt-doped Bi 25 FeO 40 / BiFeO3 nanofiber wave-absorbing materials.

[0019] The technical solutions of the application will be further described in detail below in combination with the drawings in the specification and specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The string-bead-shaped cobalt-doped Bi 25 FeO 40 XRD pattern of the / BiFeO3 nanofiber wave-absorbing material; Figure 2 The string-bead-shaped cobalt-doped Bi 25 FeO 40 SEM pattern of the / BiFeO3 nanofiber wave-absorbing material, wherein (a) is the SEM pattern of Example 1, (b) is the SEM pattern of Example 2, and (c) is the SEM pattern of Example 3; Figure 3 The string-bead-shaped cobalt-doped Bi 25 FeO 40 EDS spectrum of the / BiFeO3 nanofiber wave-absorbing material, wherein (a) is the Bi element distribution pattern, (b) is the Fe element distribution pattern, (c) is the O element distribution pattern, and (d) is the Co element distribution pattern; Figure 4 The string-bead-shaped cobalt-doped Bi 25 FeO 40 Reflection loss pattern of the / BiFeO3 nanofiber wave-absorbing material after being compounded with paraffin; Figure 5 The string-bead-shaped cobalt-doped Bi 25 FeO 40 Reflection loss pattern of the / BiFeO3 nanofiber wave-absorbing material after being compounded with paraffin; Figure 6 The string-bead-shaped cobalt-doped Bi 25 FeO 40 Reflection loss pattern of the / BiFeO3 nanofiber wave-absorbing material after being compounded with paraffin. DETAILED DESCRIPTION

[0021] The following examples are merely exemplary of a few of the various embodiments of the present application, which are only indicative of the variety of embodiments to which the present application is applicable. Unless otherwise noted, the examples provided below are illustrative only and not intended to limit the scope of the application as claimed. Various embodiments of the application, in addition to those set forth by way of example, will become apparent to those skilled in the art from the following detailed description, and the accompanying drawings.

[0022] In the present application, all the equipment and raw materials, etc. are commercially available or commonly used in the industry, unless otherwise specified. The methods in the following examples are conventional methods in the art, unless otherwise specified. Example 1

[0023] This example prepared a string-bead-shaped cobalt-doped Bi 25 FeO 40 / BiFeO3 nanofiber wave-absorbing material, its preparation process and steps are as follows: (1) 0.29 g of cobalt nitrate was dissolved in 35 mL of deionized water to obtain solution A, 0.33 g of 2-methylimidazole was dissolved in 35 mL of deionized water to obtain solution B, solution A was quickly poured into solution B, stirred uniformly and then placed for 24 h to obtain a purple precipitate; the purple precipitate was washed by centrifugation and then dried at 40℃ for 6 h to obtain a precursor; (2) 1.0034 g of bismuth nitrate and 0.788 g of iron nitrate were dissolved in 17.335 g of mixed solvent (the mixed solvent was compounded by 9.445 g of N, N-dimethylformamide and 7.89 g of anhydrous ethanol), stirred until clear and transparent, 0.05 g of the precursor was added, stirred uniformly, then 2 g of polyvinylpyrrolidone was added, and stirred at a stirring rate of 150 rpm for 8 h to obtain a spinning solution; (3) The spinning solution was electrospun, the push-in speed was set to 0.05 mm / min, the needle hole diameter was 22G, the distance between the nozzle and the rotating roller was 15 cm, the receiving speed of the rotating roller was 30 r / min, the positive voltage for spinning was 12 kV, the negative voltage was 0.5 kV, the temperature was 20℃, and the humidity was 15%, to obtain a nanofiber membrane; (4) The nanofiber membrane was placed in a vacuum drying oven, dried at a vacuum degree of 0.06 MPa and a temperature of 70℃ for 10 h; after taking out, it was placed in a muffle furnace, heated from room temperature to 300℃ at a heating rate of 5℃ / min, kept at 300℃ for 1 h, then heated from 300℃ to 550℃ at a heating rate of 5℃ / min, kept at 550℃ for 1 h, and finally cooled to room temperature at a cooling rate of 5℃ / min, to obtain a string-bead-shaped cobalt-doped Bi 25 FeO40 / BiFeO3 nanofiber wave-absorbing material. Example 2

[0024] In this example, a string-bead-shaped cobalt-doped Bi 25 FeO 40 / BiFeO3 nanofiber wave-absorbing material is prepared, and the preparation process and steps are as follows: (1) 0.29 g of cobalt nitrate is dissolved in 35 mL of deionized water to obtain solution A, 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 uniformly, it is left to stand for 20 h to obtain a purple precipitate; the purple precipitate is washed by centrifugation and dried at 60 ℃ for 4 h to obtain a precursor; (2) 1.0034 g of bismuth nitrate and 0.768 g of iron nitrate are dissolved in 17.335 g of a mixed solvent (the mixed solvent is compounded by 9.445 g of N, N-dimethylformamide and 7.89 g of anhydrous ethanol), stirred until clear and transparent, 0.1 g of the precursor is added, stirred uniformly, and then 2 g of polyvinylpyrrolidone is added, stirred at a stirring speed of 300 rpm for 14 h to obtain a spinning solution; (3) The spinning solution is electrospun, the push injection speed is set to 0.15 mm / min, the needle hole diameter is 20G, the distance between the nozzle and the rotating roller is 20 cm, the receiving speed of the rotating roller is 20 r / min, the positive voltage for spinning is 15 kV, the negative voltage is 2 kV, the temperature is 25 ℃, and the humidity is 25%, and a nanofiber membrane is obtained; (4) The nanofiber membrane is placed in a vacuum drying box and dried at a vacuum degree of 0.06 MPa and a temperature of 60 ℃ for 12 h; after taking out, it is placed in a muffle furnace, heated from room temperature to 300 ℃ at a heating rate of 3 ℃ / min, kept for 2 h, then heated from 300 ℃ to 550 ℃ at a heating rate of 3 ℃ / min, kept for 2 h, and finally cooled to room temperature at a cooling rate of 3 ℃ / min, to obtain a string-bead-shaped cobalt-doped Bi 25 FeO 40 / BiFeO3 nanofiber wave-absorbing material. Example 3

[0025] In this example, a string-bead-shaped cobalt-doped Bi 25 FeO 40 / BiFeO3 nanofiber wave-absorbing material is prepared, and the preparation process and steps are as follows: (1) 0.29 g of cobalt nitrate was dissolved in 35 mL of deionized water to obtain solution A, 0.33 g of 2-methylimidazole was dissolved in 35 mL of deionized water to obtain solution B, solution A was quickly poured into solution B, and after stirring uniformly, it was left to stand for 12 h to obtain a purple precipitate; the purple precipitate was washed by centrifugation and dried at 70℃ for 2 h to obtain a precursor; (2) 1.0034 g of bismuth nitrate and 0.747 g of iron nitrate were dissolved in 17.335 g of a mixed solvent (the mixed solvent was compounded by 9.445 g of N, N-dimethylformamide and 7.89 g of anhydrous ethanol), after stirring to be clear and transparent, 0.15 g of the precursor was added, and after stirring uniformly, 2 g of polyvinylpyrrolidone was added, and stirring was carried out at a stirring speed of 450 rpm for 10 h to obtain a spinning solution; (3) The spinning solution was electrospun, the push injection speed was set to 0.2 mm / min, the needle hole diameter was 25G, the distance between the nozzle and the rotating roller was 25 cm, the receiving speed of the rotating roller was 60 r / min, the positive voltage for spinning was 18 kV, the negative voltage was 3 kV, the temperature was 30℃, and the humidity was 30%, and a nanofiber membrane was obtained; (4) The nanofiber membrane was placed in a vacuum drying oven, dried at a vacuum degree of 0.06 MPa and a temperature of 80℃ for 8 h; after taking out, it was placed in a muffle furnace, and the temperature was raised from room temperature to 300℃ at a rate of 1℃ / min, and then kept at 300℃ for 3 h, and then raised from 300℃ to 550℃ at a rate of 1℃ / min, and kept at 550℃ for 3 h, and finally reduced to room temperature at a rate of 1℃ / min, to obtain a string-shaped cobalt-doped Bi 25 FeO 40 / BiFeO3 nanofiber wave-absorbing material. Comparative Example

[0026] In order to explore the influence of different parameters or preparation methods in the preparation process of the present application on the performance of the product of the present application, the following comparative experiments were carried out, and different wave-absorbing materials were prepared in the following comparative examples: Comparative Example 1 A wave-absorbing material was prepared in this comparative example, and the preparation process was similar to that of Example 1, except that in step (4), instead of using a segmented calcination, the temperature was directly raised from room temperature to 550℃ at a rate of 5℃ / min, and then kept at 550℃ for 2 h, and then reduced to room temperature at a rate of 5℃ / min.

[0027] Comparative Example 2 A BiFeO3 wave-absorbing material was prepared in this comparative example, and the preparation process and steps were as follows: Dissolve 1.0034 g of bismuth nitrate and 0.747 g of iron nitrate in 9.445 g of N, N-dimethylformamide and 7.89 g of anhydrous ethanol, after stirring to be clear and transparent, add 2 g of polyvinylpyrrolidone, stir at a stirring rate of 450 rpm for 12 h to obtain a spinning solution; Electrospinning the spinning solution, setting the injection speed to 0.2 mm / min, the needle hole diameter to 22 G, the distance between the nozzle and the rotating roller to 15 cm, the receiving speed of the rotating roller to 30 r / min, the positive voltage for spinning to 15 kV, the negative voltage to 2 kV, the temperature to 20℃, and the humidity to 15%, to obtain a nanofiber membrane; Place the nanofiber membrane in a vacuum drying oven, dry at a vacuum degree of 0.06 MPa and a temperature of 70℃ for 10 h; Place the dried nanofiber membrane in a muffle furnace, heat from room temperature to 550℃ at a heating rate of 1℃ / min, keep the temperature for 3 h, and then cool to room temperature at a cooling rate of 1℃ / min, to obtain BiFeO3 nanofibers.

[0028] Comparative Example 3 This comparative example prepared a wave-absorbing material, and the preparation process was similar to that of Example 1, except that in step (1), cobalt nitrate was replaced by nickel nitrate, and the remaining steps and parameters were the same as those of Example 1. Performance test

[0029] A series of morphology and performance tests were conducted on the wave-absorbing materials prepared in Examples 1-3 and Comparative Examples 1-3, and the specific test results are as follows: Figure 1 The XRD pattern of the string-shaped cobalt-doped Bi 25 FeO 40 / BiFeO3 nanofiber wave-absorbing material prepared in Examples 1-3 of the present application, and it can be seen from the figure that the string-shaped cobalt-doped Bi 25 FeO 40 / BiFeO3 nanofiber was successfully prepared by the present application, and the product had good crystallinity.

[0030] Figure 2 The XRD pattern of the string-shaped cobalt-doped Bi 25 FeO 40 / BiFeO3 nanofiber wave-absorbing material prepared in Examples 1-3 of the present application, and it can be seen from the figure that the string-shaped cobalt-doped Bi 25 FeO 40The / BiFeO3 nanofiber wave-absorbing material presents a relatively uniform fiber structure, and the string-bead structure has been generated at this time; it can be observed from (b) and (c) that, with the continuous increase of the amount of the cobalt precursor, the string-bead structure presents an obvious trend of size increase and distribution densification.

[0031] Figure 3 The string-bead cobalt-doped Bi 25 FeO 40 The EDS spectrum of the / BiFeO3 nanofiber wave-absorbing material, from which it can be seen that the Bi, Fe, O and Co elements are uniformly distributed inside the material.

[0032] 0.084 g of the nanofiber wave-absorbing material prepared in Example 1-3 and 0.036 g of the paraffin prepared in Comparative Example 1-3 are weighed respectively, mixed by petroleum ether, pressed into a concentric circular ring, and then the electromagnetic parameters in the range of 2-18 GHz are tested by a vector network analyzer. Figures 4-6 The string-bead cobalt-doped Bi 25 FeO 40 The reflection loss diagram of the / BiFeO3 nanofiber wave-absorbing material, from which it can be seen that the cobalt-doped Bi 25 FeO 40 The / BiFeO3 nanofiber wave-absorbing material has the best wave-absorbing performance, and the material has rich heterogeneous interfaces, which can increase the interface polarization loss. In addition, due to its unique string-bead structure, the multiple reflection and scattering of electromagnetic waves can be increased, so that the minimum reflection loss reaches-56.01 dB and the effective absorption band width is 6.32 GHz when the thickness is 2.33 mm.

[0033] The following table is the minimum reflection loss and effective absorption band width of the wave-absorbing materials prepared in Comparative Example 1-3 when the thickness is 2.33 mm, and the specific values are as follows: ,

[0034] From the above table and Figures 4-6 It can be seen that, compared with Comparative Example 1-3, the Bi 25 FeO 40The wave-absorbing performance of the BiFeO3 nanofiber wave-absorbing material is significantly improved and the bandwidth is increased, which is due to the fact that the segmented temperature rising can better keep the formation of the string-bead-shaped morphology, the addition of cobalt nitrate introduces a hetero-interface, increases the interface polarization, and the introduction of the magnetic metal also improves the impedance matching. The comparative example 1 has a one-step temperature rising, so that the fiber structure collapses, resulting in a decline in the wave-absorbing performance; the BiFeO3 wave-absorbing material prepared in the comparative example 2 has a single polarization mechanism, so that the wave-absorbing performance of the material is reduced; the comparative example 3 uses nickel nitrate, so that the magnetic property is not as good as that of cobalt, and there is no good impedance matching, thus resulting in a decline in the wave-absorbing performance.

[0035] Finally, it should be noted that: the above only for the preferred embodiments of the present application, and not for limiting the present application, although the foregoing embodiments of the present application are described in detail, for those skilled in the art, it still can be modified, or part of the technical features of the equivalent replacement. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application, should be included in the scope of protection of the claims of the present application.

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 thereto. 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 subjected to electrospinning 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 is obtained.

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 (2), the mass ratio of bismuth nitrate to iron nitrate, mixed solvent, precursor, and spinning aid is 1.0034:(0.747-0.788):17.335:(0.05-0.15):

2.

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 (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%.

6. The bead-like Co-doped Bi < 2 Fe < 1 O < 6 > of claim 1. 25 FeO 40 The application discloses a preparation method of a bead-like Co-doped Bi < 2 Fe < 1 O < 6 > nanofiber wave-absorbing material. In step (4), the drying temperature is 60-80 ℃, the time is 8-12 h, and the vacuum degree is 0.06 MPa.

7. 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 calcination process is carried out in sequence according to the following steps: (a) The first temperature rising stage: the temperature is raised from room temperature to 300 ℃ at a rate of 1-5 ℃ / min, and the temperature is maintained for 1-3 h; (b) The second temperature rising stage: the temperature is raised from 300 ℃ to 550 ℃ at a rate of 1-5 ℃ / min, and the temperature is maintained for 1-3 h; (c) The temperature lowering stage: the temperature is lowered to room temperature at a rate of 1-5 ℃ / min.

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