Preparation method of wheat-ear-shaped bismuth ferrite nanofiber absorbing material

Abstract

The invention discloses a method for preparing a wheat-ear-shaped bismuth ferrite nanofiber absorbing material. The method utilizes a sol-gel method in conjunction with an electrostatic spinning process to prepare bismuth ferrite nanofibers. During the preparation of a precursor solution by the sol-gel method, a compound additive consisting of ethylene glycol methyl ether, N-methyl pyrrolidone, acetic acid, citric acid, and isopropyl alcohol is added. The wheat-ear-shaped bismuth ferrite nanofiber absorbing material is then obtained through electrostatic spinning, drying, and calcination. The preparation process of the invention is simple and the preparation cost is low. When the prepared wheat-ear-shaped bismuth ferrite nanofiber absorbing material has a thickness of 3 mm and a frequency of 12.24 GHz, the minimum reflection loss reaches 36.9 dB, and the effective absorption bandwidth is 6.32 GHz.

Description

Technical Field

[0001] The invention belongs to the field of nanofiber wave-absorbing materials and relates to a method for preparing wheat-ear-shaped bismuth ferrite nanofiber wave-absorbing material. Background Art

[0002] The rapid development of wireless technology has led to the emergence of sophisticated electronic devices. The electromagnetic waves they generate can pose a threat to human health, making electromagnetic pollution a new form of environmental pollution. Microwave absorbing materials, as important functional materials for absorbing and attenuating incident electromagnetic waves, have a wide range of applications in both civilian and military fields. Currently, in addition to research on the composition of microwave absorbing materials, their structural design is also a hot topic in this field. Among the various structures, one-dimensional structures have attracted widespread attention due to their unique shape anisotropy and spatial confinement effects.

[0003] Electrospinning technology has been widely used to produce one-dimensional nanofibers with high aspect ratios. In the field of electromagnetic wave absorption, high aspect ratio fiber structures have a significant impact on the material's attenuation capacity and impedance matching. These fibers can be constructed into three-dimensional network structures, which are believed to facilitate multiple scattering of electromagnetic waves, thereby dissipating a certain amount of electromagnetic wave energy before entering the material. Furthermore, high aspect ratio fiber structures facilitate the directional movement of electrons, forming microcurrents. Due to their inherent electrical resistance, these microcurrents dissipate electromagnetic waves as heat, thereby increasing microwave absorption capacity.

[0004] A good microwave absorbing material must meet two basic requirements: first, electromagnetic matching properties. When an electromagnetic wave is incident on the surface of the absorbing material, the absorbing material absorbs the electromagnetic wave energy and reduces its reflection. Second, the absorbing material's attenuation properties must be considered. This requires that the electromagnetic wave energy be absorbed and reduced as soon as it enters the material. Bismuth ferrite (BiFeO3, BFO) is a multiferroic material with a rhombohedral perovskite structure belonging to the R3c space group. Its ferroelectric and ferromagnetic properties coexist at room temperature, facilitating electromagnetic matching and, therefore, holding significant potential for microwave absorption. However, current bismuth ferrite nanomaterials have a narrow absorption band, making them difficult to meet the broadband absorption requirements of modern microwave absorbing materials. Furthermore, their absorption strength is limited, lagging behind some high-performance absorbing materials. Furthermore, bismuth ferrite nanomaterials suffer from poor impedance matching, resulting in relatively large reflections from their surfaces and relatively little absorption within the material, thus compromising their overall microwave absorption performance.

[0005] Based on this, the present invention adds a compound additive during the preparation process of bismuth ferrite nanofibers to prepare wheat-ear-shaped bismuth ferrite nanofibers, which have good application prospects in the field of wave absorption. Summary of the Invention

[0006] In response to the above technical problems, the present invention aims to provide a method for preparing wheat-ear-shaped bismuth ferrite nanofiber absorbing material. The method uses a sol-gel method combined with an electrospinning process to prepare bismuth ferrite nanofibers. In the process of preparing the precursor solution by the sol-gel method, a compound additive consisting of ethylene glycol methyl ether, N-methyl pyrrolidone, acetic acid, citric acid and isopropyl alcohol is added, and then the wheat-ear-shaped bismuth ferrite nanofiber absorbing material is obtained by electrospinning, drying and calcining. The preparation process of the present invention is simple and the preparation cost is low. When the prepared wheat-ear-shaped bismuth ferrite nanofiber absorbing material has a thickness of 3 mm and a frequency of 12.24 GHz, the minimum reflection loss reaches -36.9 dB, and the effective absorption bandwidth is 6.32 GHz.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] A method for preparing a wheat-ear-shaped bismuth ferrite nanofiber absorbing material is carried out in the following steps in sequence:

[0009] (1) Dissolve bismuth nitrate pentahydrate and ferric nitrate nonahydrate in N,N-dimethylformamide, stir until clear and transparent, add compound additives, stir evenly, then add spinning aid, and stir at a stirring rate of 200-300 rpm for 7-15 hours to obtain a precursor solution;

[0010] The compound additive is ethylene glycol methyl ether, N-methyl pyrrolidone, acetic acid, citric acid and isopropyl alcohol, and the mass ratio thereof is (1-5): (1-4): (1-5) (0.1-1): (2-5);

[0011] The composite additives in the present invention act synergistically to affect the morphology of bismuth ferrite nanofibers, thereby affecting their wave absorbing performance. Specifically, ethylene glycol methyl ether and isopropyl alcohol are used as solvents. After the two are mixed, their solubility for N-methyl pyrrolidone, acetic acid, citric acid, and nitrate is enhanced. The addition of N-methyl pyrrolidone is conducive to the uniform dispersion of citric acid and metal salts in the solvent. At the same time, the polarity of the mixed solvent can be adjusted. N-methyl pyrrolidone itself is a strong polar solvent, while isopropyl alcohol and ethylene glycol methyl ether are also polar solvents, but with different degrees of polarity. N-methyl pyrrolidone can make the mixed solvent better interact with the three carboxyl groups of citric acid, thereby improving the dissolution efficiency. In addition, citric acid is used as a complexing agent, and citrate ions will react with Fe 3+ and Bi 3+ Acetic acid forms a complex, thereby controlling the formation process of the sol; acetic acid helps the colloid to form stably by adjusting the pH of the system, thereby ensuring that the fiber is not easily broken during the sintering process;

[0012] In the present invention, the mass ratio between the compound additives is crucial, as it affects the nucleation and growth process of bismuth ferrite. When the mass ratio of ethylene glycol methyl ether, N-methyl pyrrolidone, acetic acid, citric acid and isopropyl alcohol is (1-5): (1-4): (1-5) (0.1-1): (2-5), an appropriate nucleation rate and a complete wheat-ear-shaped structure can be achieved. If the mass ratio of ethylene glycol methyl ether, N-methyl pyrrolidone, acetic acid, citric acid and isopropyl alcohol is greater than this mass ratio, the growth process of bismuth ferrite nanofibers is excessively disturbed, and a regular wheat-ear-shaped structure cannot be formed. If the mass ratio of ethylene glycol methyl ether, N-methyl pyrrolidone, acetic acid, citric acid and isopropyl alcohol is less than this mass ratio, the additive ratio is insufficient, the crystallization speed and crystallization direction of the bismuth ferrite nanofibers cannot be effectively controlled, resulting in unsatisfactory crystallinity and uneven grain size, thereby affecting the overall performance of the material.

[0013] (2) electrospinning the precursor solution obtained in step (1) to obtain a bismuth ferrite nanofiber precursor;

[0014] (3) placing the bismuth ferrite nanofiber precursor obtained in step (2) in a vacuum drying oven for drying;

[0015] (4) placing the dried bismuth ferrite nanofiber precursor into a muffle furnace and calcining it to obtain a wheat-ear-shaped bismuth ferrite nanofiber absorbing material;

[0016] As a limitation of the preparation method of the present invention, in step (1), the mass ratio of the bismuth nitrate pentahydrate, the ferric nitrate nonahydrate and the N,N-dimethylformamide is 1.27:1:9.34.

[0017] As a second limitation of the preparation method of the present invention, in step (1), the spinning aid is polyvinyl pyrrolidone or polyacrylonitrile.

[0018] As a third limitation of the preparation method of the present invention, in step (1), the mass ratio of the bismuth nitrate pentahydrate, ethylene glycol methyl ether and spinning aid is 1: (0.97-4.86): (1.36-2.62).

[0019] As a fourth limitation of the preparation method of the present invention, in step (2), the electrospinning injection speed is 0.03-0.25 mm / min, the pinhole diameter is 20-25G, the distance between the nozzle and the roller is 15-25 cm, the receiving speed of the roller is 30-60 r / min, the spinning positive voltage is 13-20 kV, the negative voltage is 0.5-3 kV, the temperature is 20-35 ° C, and the humidity is 20-40%.

[0020] As a fifth limitation of the preparation method of the present invention, in step (3), the drying temperature is 60-100°C, the time is 8-12 hours, and the vacuum degree is -0.08 MPa.

[0021] As a sixth limitation of the preparation method of the present invention, in step (4), the calcination process is carried out in the following order:

[0022] (a) The first heating stage is to increase the temperature from room temperature to 260°C at a heating rate of 1-5°C / min and keep the temperature for 1-3 hours;

[0023] (b) the second heating stage, heating from 260°C to 340°C at a heating rate of 1-5°C / min and holding for 1-3 h;

[0024] (c) the third heating stage, heating from 340°C to 500°C at a heating rate of 1-5°C / min and holding for 1-3 h;

[0025] (d) Cooling stage, cooling to room temperature with the furnace;

[0026] The calcination process in the present invention is crucial for the morphology formation of bismuth ferrite nanofibers. When the temperature is increased from room temperature to 260°C at a heating rate of 1-5°C / min, the surface adsorbed water first decomposes, then the nitrate loses part of the bound water, some unstable groups on the side chain of polyvinyl pyrrolidone break, and its bonding effect in the bismuth ferrite fiber gradually weakens. Due to the introduction of the compound additive, ethylene glycol methyl ether and isopropyl alcohol evaporate early during the sintering process, which will generate certain pores inside the fiber, providing space for the subsequent formation of wheat ear-shaped structures. The volatilization process will affect the N, N-dimethylformamide, N-methylpyrrolidone and acetic acid. The distribution and movement of the fibers cause the concentration of local particles in the fibers to change, which is helpful for the initial shaping of the fiber morphology. At the same time, the volatilization of acetic acid and N, N-dimethylformamide can promote the rearrangement of the surrounding ethylene glycol methyl ether and N-methylpyrrolidone molecules, and the concentrations of bismuth nitrate pentahydrate and ferric nitrate nonahydrate increase relatively. Bismuth ferrite will nucleate in the local supersaturated area, affecting the morphological arrangement of the fibers. N-methylpyrrolidone has a high boiling point and evaporates relatively late in the sintering process. As the temperature rises, bismuth nitrate pentahydrate and ferric nitrate nonahydrate particles will slowly evaporate with N-methylpyrrolidone to form internal crystal nuclei. In addition, during the sintering process, citrate ions react with Fe 3+ and Bi 3+The formed complex also slowly decomposes, causing the outward growth rate of the metal particles during sintering to exceed the volatilization rate of the organic matter (mainly polyvinyl pyrrolidone), which is conducive to the growth of metal particles on the surface of the nanofibers. Holding the temperature for 1-3 hours provides sufficient time for the metal particles to grow on the fiber surface, thereby improving the crystal structure and promoting the formation of a regular wheat-ear-shaped structure. When the sintering temperature is further increased from 260°C to 340°C at a heating rate of 1-5°C / min, the polyvinyl pyrrolidone and nitrate further decompose, and the nucleated bismuth ferrite particles grow along the diffusion direction of the solute (bismuth nitrate pentahydrate and ferric nitrate nonahydrate). Due to the volatilization of the solvent (ethylene glycol methyl ether, isopropyl alcohol, N,N-dimethylformamide, N-methylpyrrolidone and acetic acid) from different locations within and on the fiber surface and at different volatilization rates, the bismuth ferrite grows at different speeds and directions at different locations, resulting in small wheat-ear-shaped grains. Holding the temperature for 1-3 hours promotes the growth of small wheat-ear-shaped grains. When the sintering temperature continues to increase from 340°C to 500°C at a heating rate of 1-5°C / min, the decomposition reaction of polyvinyl pyrrolidone intensifies, the main chain breaks in large numbers, the bismuth ferrite grains diffuse and grow, and the metal particles on the fiber surface transform from an amorphous phase to a perovskite phase, eventually presenting a fiber morphology similar to wheat ears. Holding the temperature for 1-3 hours provides sufficient time for the diffusion of atoms, making the crystal boundaries of the wheat ear structure more regular.

[0027] The present invention also provides an application of the wheat-ear-shaped bismuth ferrite nanofiber wave-absorbing material. The prepared wheat-ear-shaped bismuth ferrite nanofiber is applied in the field of wave-absorbing materials.

[0028] The above technical solution of the present invention is taken as a whole, and the various steps are closely related and influence each other, which jointly determine the morphological characteristics and performance of the product.

[0029] The above technical solution has the following advantages or beneficial effects:

[0030] 1. The wheat-ear-shaped bismuth ferrite nanofibers prepared by the present invention based on the sol-gel method and electrospinning process have a unique morphology and good microwave absorption performance;

[0031] 2. The wheat-ear-shaped bismuth ferrite nanofiber absorbing material prepared by the present invention has a minimum reflection loss of -36.9 dB at a thickness of 3 mm and a frequency of 12.24 GHz, and an effective absorption bandwidth of 6.32 GHz;

[0032] 3. The present invention has simple process, low cost, excellent wave absorbing performance, and good application prospects in the field of wave absorbing.

[0033] The invention is suitable for preparing wheat-ear-shaped bismuth ferrite nanofiber wave absorbing materials.

[0034] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The XRD patterns of the bismuth ferrite nanofibers prepared in Example 1 and Comparative Examples 1-2 of the present invention are shown;

[0036] Figure 2 The SEM images of bismuth ferrite nanofibers prepared in Example 1 and Comparative Examples 1-2 of the present invention are shown;

[0037] Figure 3 This is a reflection loss diagram of the absorbing material composited with bismuth ferrite nanofibers and paraffin prepared in Example 1 of the present invention and Comparative Examples 1-2. DETAILED DESCRIPTION

[0038] The following embodiments are merely some of the embodiments of the present invention, rather than all of them. Therefore, the detailed description of the embodiments of the present invention provided below is not intended to limit the scope of the claimed invention, but rather merely represents selected embodiments of the present invention. All other embodiments derived by those skilled in the art based on the embodiments of the present invention without creative effort are intended to fall within the scope of protection of the present invention.

[0039] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments, unless otherwise specified, are all conventional methods in the art.

[0040] Example 1

[0041] This embodiment prepares a wheat-ear-shaped bismuth ferrite nanofiber absorbing material, and the preparation process and steps are as follows:

[0042] (1) 1.029 g of bismuth nitrate pentahydrate and 0.808 g of ferric nitrate nonahydrate were dissolved in 7.55 g of N,N-dimethylformamide and stirred until clear and transparent. Then, a compound additive (the compound additive was 3 g of ethylene glycol methyl ether, 1 g of N-methylpyrrolidone, 2 g of acetic acid, 0.8 g of citric acid and 4 g of isopropyl alcohol) was added. After stirring evenly, 1.8 g of polyvinylpyrrolidone was added. After stirring at a stirring rate of 200 rpm for 7 h, a precursor solution was obtained.

[0043] (2) electrospinning the precursor solution obtained in step (1) to obtain a bismuth ferrite nanofiber precursor, setting the electrospinning injection speed to 0.03 mm / min, the needle hole diameter to 20G, the distance between the nozzle and the roller to 15 cm, the receiving speed of the roller to 30 r / min, the spinning positive voltage to 13 kV, the negative voltage to 0.5 kV, the temperature to 20 ° C, and the humidity to 20%;

[0044] (3) placing the bismuth ferrite nanofiber precursor obtained in step (2) in a vacuum drying oven and drying at 60° C. for 12 h with a vacuum degree of -0.08 MPa;

[0045] (4) The dried bismuth ferrite nanofiber precursor was placed in a muffle furnace, first heated from room temperature to 260°C at a heating rate of 1°C / min, kept warm for 1 hour, then heated from 260°C to 340°C at a heating rate of 1°C / min, kept warm for 1 hour, then heated from 340°C to 500°C at a heating rate of 1°C / min, kept warm for 1 hour, and finally cooled to room temperature with the furnace to obtain wheat-ear-shaped bismuth ferrite nanofiber absorbing material.

[0046] Example 2

[0047] This embodiment prepares a wheat-ear-shaped bismuth ferrite nanofiber absorbing material, and the preparation process and steps are as follows:

[0048] (1) 1.029 g of bismuth nitrate pentahydrate and 0.808 g of ferric nitrate nonahydrate were dissolved in 7.55 g of N,N-dimethylformamide and stirred until clear and transparent. Then, a composite additive (the composite additive was 1 g of ethylene glycol methyl ether, 2 g of N-methylpyrrolidone, 1 g of acetic acid, 0.1 g of citric acid and 2 g of isopropyl alcohol) was added and stirred evenly. Then, 1.4 g of polyvinylpyrrolidone was added and stirred at a stirring rate of 250 rpm for 12 h to obtain a precursor solution.

[0049] (2) electrospinning the precursor solution obtained in step (1) to obtain a bismuth ferrite nanofiber precursor, setting the electrospinning injection speed to 0.15 mm / min, the pinhole diameter to 22G, the distance between the nozzle and the roller to 20 cm, the receiving speed of the roller to 50 r / min, the spinning positive voltage to 15 kV, the negative voltage to 2 kV, the temperature to 30 ° C, and the humidity to 30%;

[0050] (3) placing the bismuth ferrite nanofiber precursor obtained in step (2) in a vacuum drying oven and drying at 80° C. for 10 h with a vacuum degree of -0.08 MPa;

[0051] (4) The dried bismuth ferrite nanofiber precursor was placed in a muffle furnace, first heated from room temperature to 260°C at a heating rate of 3°C / min, kept warm for 2 h, then heated from 260°C to 340°C at a heating rate of 3°C / min, kept warm for 2 h, then heated from 340°C to 500°C at a heating rate of 3°C / min, kept warm for 2 h, and finally cooled to room temperature with the furnace to obtain wheat-ear-shaped bismuth ferrite nanofiber absorbing material.

[0052] Example 3

[0053] This embodiment prepares a wheat-ear-shaped bismuth ferrite nanofiber absorbing material, and the preparation process and steps are as follows:

[0054] (1) 1.029 g of bismuth nitrate pentahydrate and 0.808 g of ferric nitrate nonahydrate were dissolved in 7.55 g of N,N-dimethylformamide and stirred until clear and transparent. Then, a compound additive (the compound additive was 5 g of ethylene glycol methyl ether, 4 g of N-methylpyrrolidone, 5 g of acetic acid, 1 g of citric acid and 5 g of isopropyl alcohol) was added. After stirring evenly, 2.7 g of polyvinylpyrrolidone was added. After stirring at a stirring rate of 300 rpm for 15 h, a precursor solution was obtained.

[0055] (2) electrospinning the precursor solution obtained in step (1) to obtain a bismuth ferrite nanofiber precursor, setting the electrospinning injection speed to 0.25 mm / min, the pinhole diameter to 25G, the distance between the nozzle and the roller to 25 cm, the receiving speed of the roller to 60 r / min, the spinning positive voltage to 20 kV, the negative voltage to 3 kV, the temperature to 35 ° C, and the humidity to 40%;

[0056] (3) placing the bismuth ferrite nanofiber precursor obtained in step (2) in a vacuum drying oven and drying it at 100° C. for 8 h with a vacuum degree of -0.08 MPa;

[0057] (4) The dried bismuth ferrite nanofiber precursor was placed in a muffle furnace, first heated from room temperature to 260°C at a heating rate of 5°C / min, kept warm for 3 h, then heated from 260°C to 340°C at a heating rate of 5°C / min, kept warm for 3 h, then heated from 340°C to 500°C at a heating rate of 5°C / min, kept warm for 3 h, and finally cooled to room temperature with the furnace to obtain wheat-ear-shaped bismuth ferrite nanofiber absorbing material.

[0058] Comparative Example

[0059] In order to explore the effects of different parameters and different additives in the preparation process of the present invention on the performance of the product of the present invention, the following comparative experiments were conducted. Different bismuth ferrite nanofibers were prepared in the following comparative examples, as follows:

[0060] Comparative Example 1

[0061] In this comparative example, bismuth ferrite nanofibers similar to those in Example 1 were prepared, with the only difference being that, in step (1), no compound additive was added, and the remaining parameters were the same as those in Example 1.

[0062] Comparative Example 2

[0063] In this comparative example, bismuth ferrite nanofibers similar to those in Example 1 were prepared, except that only acetic acid was added to the compound additive in step (1), and the remaining parameters were the same as those in Example 1.

[0064] Comparative Example 3

[0065] In this comparative example, bismuth ferrite nanofibers similar to those in Example 1 were prepared, except that ethylene glycol methyl ether was not added to the compound additive in step (1). The remaining parameters were the same as those in Example 1.

[0066] Comparative Example 4

[0067] In this comparative example, bismuth ferrite nanofibers similar to those in Example 1 were prepared, except that isopropyl alcohol was not added to the compound additive in step (1), and the other parameters were the same as those in Example 1.

[0068] Comparative Example 5

[0069] In this comparative example, bismuth ferrite nanofibers similar to those in Example 1 were prepared, except that citric acid was not added to the compound additive in step (1). The remaining parameters were the same as those in Example 1.

[0070] Comparative Example 6

[0071] In this comparative example, bismuth ferrite nanofibers similar to those in Example 1 were prepared, except that N-methylpyrrolidone was not added to the compound additive in step (1), and the other parameters were the same as those in Example 1.

[0072] Comparative Example 7

[0073] This comparative example prepares bismuth ferrite nanofibers similar to those in Example 1, except that in step (3), the calcination process does not adopt a staged heating method, but is directly heated from room temperature to 500°C at a heating rate of 5°C / min.

[0074] Performance Testing

[0075] 0.0975 g of the bismuth ferrite nanofibers prepared in Examples 1-3 and Comparative Examples 1-7 were respectively weighed and mixed with 0.0525 g of paraffin wax, and pressed into concentric rings. The electromagnetic parameters were tested using a vector network analyzer to obtain the wave absorbing properties.

[0076] like Figure 1 , which is the XRD diagram of the bismuth ferrite nanofibers prepared in Example 1 and Comparative Examples 1-2 of the present invention. It can be seen from the figure that the bismuth ferrite nanofibers prepared in Example 1 and Comparative Examples 1-2 have obvious rhombohedral perovskite structure, the product has good crystallinity, and no impurity phase is generated.

[0077] Figure 2This is the SEM image of the bismuth ferrite nanofibers prepared in Example 1 of the present invention and Comparative Examples 1-2. From the figure, it can be seen that due to the unstable sol state of Comparative Examples 1 and 2, the metal salts are unevenly dispersed in the sol, presenting block-like and short rod-like morphologies, while Example 1 presents a wheat ear-like structure.

[0078] Figure 3 This is a reflection loss diagram of the bismuth ferrite nanofiber and paraffin composite absorbing material prepared in Example 1 of the present invention and Comparative Examples 1-2. As can be seen from the figure, the bismuth ferrite nanofiber with a wheat-ear-shaped structure prepared in Example 1 has the best absorbing performance. The unique wheat-ear structure and the constructed three-dimensional network structure of this material can achieve multiple reflections and absorption of electromagnetic waves, thereby achieving a minimum reflection loss of -36.9 dB at a thickness of 3 mm and a frequency of 12.24 GHz, and an effective absorption bandwidth of 6.32 GHz. Compared with Comparative Examples 1 and 2, the bandwidth of the absorbing material prepared in Example 1 is increased, and the absorbing performance is significantly improved.

[0079] The following table shows the minimum reflection loss and effective absorption bandwidth of the bismuth ferrite nanofibers prepared in Examples 2-3 and Comparative Examples 3-7 when the thickness is 3 mm. The specific values ​​are as follows:

[0080] Minimum reflection loss (dB) Effective absorption bandwidth (GHz) Example 2 -33.86 7.68 Example 3 -29.06 6.32 Comparative Example 3 -20.7 5.44 Comparative Example 4 -15.66 6.96 Comparative Example 5 -13.8 4.48 Comparative Example 6 -14.9 4.72 Comparative Example 7 -18.94 5.12

[0081] From the above table and Figure 3 It can be seen that compared with comparative examples 1-7, the wave absorbing performance of the wheat-ear-shaped nanofibers prepared in examples 1-3 is significantly improved and the bandwidth is increased.

[0082] 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 aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing wheat-ear-shaped bismuth ferrite nanofiber absorbing material, characterized in that: Follow the steps below in order: (1) Dissolve bismuth nitrate pentahydrate and ferric nitrate nonahydrate in N,N-dimethylformamide, stir until clear and transparent, add compound additives, stir evenly, then add spinning aids, stir at a stirring rate of 200-300 rpm for 7-15 h to obtain a precursor solution; The spinning aid is polyvinyl pyrrolidone or polyacrylonitrile; The compound additives are ethylene glycol methyl ether, N-methyl pyrrolidone, acetic acid, citric acid and isopropyl alcohol, and the mass ratio thereof is (1-5): (1-4): (1-5) (0.1-1): (2-5); The mass ratio of the bismuth nitrate pentahydrate, ferric nitrate nonahydrate and N,N-dimethylformamide is 1.27:1:9.34; The mass ratio of the bismuth nitrate pentahydrate, ethylene glycol methyl ether and spinning aid is 1: (0.97-4.86): (1.36-2.62); (2) electrospinning the precursor solution obtained in step (1) to obtain a bismuth ferrite nanofiber precursor; (3) placing the bismuth ferrite nanofiber precursor obtained in step (2) in a vacuum drying oven for drying; (4) placing the dried bismuth ferrite nanofiber precursor into a muffle furnace and calcining it to obtain a wheat-ear-shaped bismuth ferrite nanofiber absorbing material; The calcination process is carried out in the following order: (a) The first heating stage is to increase the temperature from room temperature to 260°C at a heating rate of 1-5°C / min and keep the temperature for 1-3 h; (b) The second heating stage: heating from 260°C to 340°C at a heating rate of 1-5°C / min and holding for 1-3 h; (c) The third heating stage: heating from 340°C to 500°C at a heating rate of 1-5°C / min and holding for 1-3 h; (d) Cooling stage: cooling to room temperature along with the furnace.

2. The method for preparing a wheat-ear-shaped bismuth ferrite nanofiber absorbing material according to claim 1, characterized in that: In step (2), the electrospinning injection speed is 0.03-0.25 mm / min, the pinhole diameter is 20-25 G, the distance between the nozzle and the roller is 15-25 cm, the receiving speed of the roller is 30-60 r / min, the spinning positive voltage is 13-20 kV, the negative voltage is 0.5-3 kV, the temperature is 20-35°C, and the humidity is 20-40%.

3. The method for preparing a wheat-ear-shaped bismuth ferrite nanofiber absorbing material according to claim 1, characterized in that: In step (3), the drying temperature is 60-100°C, the drying time is 8-12 h, and the vacuum degree is -0.08 MPa.

4. The method for preparing the wheat-ear-shaped bismuth ferrite nanofiber absorbing material according to any one of claims 1 to 3, characterized in that: The prepared wheat-ear-shaped bismuth ferrite nanofibers are used in the field of wave-absorbing materials.

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