V2O5 filled carbon nanofiber composite material with three-dimensional network structure as well as preparation and application of V2O5 filled carbon nanofiber composite material

Abstract

The invention provides a V2O5 filled carbon nanofiber composite material with a three-dimensional network structure as well as preparation and application of the V2O5 filled carbon nanofiber composite material. The composite material comprises a three-dimensional skeleton formed by carbon nanofibers and V2O5 nanoparticles dispersed in the three-dimensional skeleton in an embedded form. Wherein the diameter of the carbon nanofibers ranges from 200 nanometers to 300 nanometers, and the particle size of the V2O5 nanoparticles ranges from 300 nanometers to 400 nanometers. The electromagnetic wave absorbing material with the three-dimensional network structure is reported for the first time, and is not reported in the prior art. Moreover, based on the three-dimensional network structure, the composite material shows excellent electromagnetic wave absorption performance, the minimum reflection loss (-67.93 dB) equivalent to or even better than that in the prior art can be achieved on the premise that the thickness (1.25 mm) of the material is reduced, the requirements of light and thin-layer electromagnetic wave absorption materials are met, the application prospect is wide, and economic benefits are considerable. The invention further provides a preparation method of the V2O5 filled carbon nanofiber composite material and application of the V2O5 filled carbon nanofiber composite material in the field of electromagnetic wave absorption.

Description

Technical Field

[0001] The present invention belongs to the field of materials, and relates to an electromagnetic wave absorbing material, in particular to a V2O5-filled carbon nanofiber composite material with a three-dimensional network structure and its preparation and application. Background Art

[0002] Due to the rapid development of information and technology, electronic devices and related devices using electromagnetic waves as a transmission medium are constantly being updated and widely used. However, the generated electromagnetic radiation poses a serious threat to military security and human health. With the advent of the 5G era and the rapid development of electronic devices, the problem of electromagnetic pollution is becoming increasingly serious. Developing efficient electromagnetic wave absorbing materials has become the key to solving electromagnetic interference (EMI) and electromagnetic radiation problems. Electromagnetic wave absorbing materials can convert the incident electromagnetic wave energy into heat energy or other forms of energy dissipation, thereby effectively reducing the reflection and transmission of electromagnetic waves. In order to achieve effective absorption of electromagnetic waves, such materials not only need to have characteristics such as light weight, thin layer, wide frequency band, and strong absorption, but also need to achieve effective electromagnetic wave attenuation without increasing the equipment load.

[0003] Carbon-based materials have received extensive attention in the field of electromagnetic wave absorption due to their excellent electrical conductivity, low density, and diverse morphologies. They also have good chemical flexibility and can further optimize the material properties through different doping or composite methods. However, traditional carbon fiber absorbing materials have certain limitations in loss paths and impedance matching, making it difficult to meet the requirements of more efficient absorbing materials.

[0004] Vanadium (V) oxide, as a typical transition metal oxide, has received extensive attention due to its multivalence and open framework crystal structure, and has made great progress in various fields, such as rechargeable zinc-ion batteries, smart windows, and thermochromic smart coatings. However, in the field of EMA, there are few reports on pure V-type oxides. There is no relevant report in the prior art on preparing materials with excellent electromagnetic wave absorption performance using vanadium (V) oxide. Summary of the Invention

[0005] In view of the current situation of electromagnetic wave absorbing materials in the prior art, the present invention provides a V2O5-filled carbon nanofiber composite material with a three-dimensional network structure, as well as its preparation method and application. This application reports for the first time a wave-absorbing composite material with V2O5 as the wave-absorbing agent filled in carbon nanofibers. Moreover, the composite material forms a three-dimensional network structure connected by V2O5 nodes, overcoming the technical prejudice in the structure of electromagnetic wave absorbing materials in the prior art. Not only that, based on the three-dimensional network structure, the composite material exhibits excellent electromagnetic wave absorption performance. On the premise of reducing the material thickness (1.25 mm), it can achieve a minimum reflection loss (-67.93 dB) equivalent to or even better than that of the prior art, meeting the requirements of lightweight and thin-layer electromagnetic wave absorbing materials, and having broad application prospects and considerable economic benefits.

[0006] The technical solution of the present invention:

[0007] A V2O5-filled carbon nanofiber composite material with a three-dimensional network structure, the composite material includes a three-dimensional skeleton composed of carbon nanofibers and V2O5 nanoparticles dispersed in the three-dimensional skeleton in an embedded form. Among them, the diameter of the carbon nanofibers is 200-300 nanometers, and the particle size of the V2O5 nanoparticles is 300-400 nanometers.

[0008] The significant difference from the carbon fiber composite wave-absorbing materials reported in the prior art is as follows: First, a three-dimensional network structure composite wave-absorbing material with V2O5-filled carbon fibers is prepared. In this application, V2O5 is first used as a wave-absorbing agent to be compounded with carbon nanofibers to prepare a composite wave-absorbing material. V2O5 is not only uniformly dispersed in the carbon nanofibers in the form of small-sized particles, but also can aggregate into nodes with larger particle sizes to connect the carbon fibers into a three-dimensional network structure, which has better electromagnetic wave transmission performance compared with the three-dimensional network structure formed by the mutual overlap of the previously reported one-dimensional materials. Second, the electromagnetic wave absorption performance of the composite material has been significantly improved. When the thickness of the material is only 1.25 mm, which is much lower than that of traditional materials (>2 mm), and it still maintains good electromagnetic wave absorption performance (the minimum reflection loss is -67.93 dB, and the effective absorption bandwidth is 3.94 GHz), achieving unexpected technical effects. The inventor speculates that this is because the three-dimensional network structure of this composite material, which is significantly different from other carbon-based composite materials, effectively increases the reflection and scattering paths of electromagnetic waves inside the material, promotes the absorption and attenuation of electromagnetic waves; therefore, it greatly reduces the thickness of the material, meets the current requirements for lightweight and ultra-thin electromagnetic wave absorbing materials, effectively reduces the burden on equipment, and meets the lightweight requirements.

[0009] The preparation method of the V2O5-filled carbon nanofiber composite material as described above includes the following steps:

[0010] (1) Preparation of the precursor solution: Appropriate amounts of V2O5 nanoparticles and PANF were taken and stirred at 30 - 60 °C for 20 h and dissolved in DMF to obtain the precursor solution. Among them, the weight ratio of the V2O5 nanoparticles to PANF was 2:16 - 4:16. Vanadium pentoxide (V2O5), as a transition metal oxide, has a unique layered structure and adjustable electronic properties. However, the conductive loss of single V2O5 is insufficient and it is difficult to achieve efficient absorption; moreover, the interfacial polarization effect of traditional composite materials is weak, resulting in limited energy loss.

[0011] (2) Electrospinning: The precursor solution prepared in step (1) was transferred to a spinning device for electrospinning, and the product was collected to obtain V2O5 / PANF. Among them, the voltage of the electrospinning was set at 22 - 26 kV, and the distance between the needle and the collector was 13 - 17 cm. The nanofibers prepared by the electrospinning technique have a high specific surface area, high porosity, and good mechanical properties.

[0012] (3) Carbonization treatment: After the product obtained in step (2) was dried and pre-carbonized, it was carbonized under an inert gas atmosphere at a temperature of 700 °C - 900 °C for 2 - 4 hours to obtain V2O5 / CNF, that is, a V2O5-filled carbon nanofiber composite material with a three-dimensional network structure. The product was put into a mortar and ground into a powder state and stored in a dry condition. Among them, the specific drying treatment was: drying at 50 - 60 °C for 12 - 14 h to obtain dry nanofibers; the specific pre-carbonization was: heating at 280 - 300 °C for 1 - 2 hours.

[0013] The V2O5 / CNF network structure composite material was prepared through the aforementioned electrospinning and high-temperature carbonization, and its electromagnetic wave absorption performance was significantly improved.

[0014] Preferably, both the pre-carbonization step and the carbonization step were carried out with a uniform heating rate, and the heating rate was 3 - 5 °C / min.

[0015] Preferably, the V2O5 was prepared by a hydrothermal method, and the specific operation was as follows: First, an 80 mL mixed solution of ethanol and water (C2H5OH:H2O = 1:9 [v:v]) was prepared. Then 0.3 g of NH4VO3 was dissolved in the mixed solution, denoted as solution A. It was ultrasonicated for 0.5 h until completely dissolved. Then a 5% hydrochloric acid solution was prepared, denoted as solution B. Solution B was added dropwise to solution A while stirring until the pH was adjusted to 3. The above solution was transferred to a stainless steel autoclave and reacted at 140 °C for 20 h. The product was washed three times alternately with ethanol and water and dried overnight at 80 °C to obtain V2O5. The dried V2O5 was put into a mortar and ground into a powder state and stored in a dry condition.

[0016] By adopting the preparation method described in the present invention, V2O5 and CNF are introduced into the composite nanomaterial. The inventor unexpectedly found that the prepared composite nanomaterial has a three-dimensional network structure, specifically: V2O5 nanoparticles are dispersed in the three-dimensional skeleton composed of carbon nanofibers in an embedded form. Under this structure, CNF with high conductivity forms a continuous conductive network. V2O5, as a semiconductor oxide, forms a heterogeneous interface with CNF to promote charge migration, and the two achieve a synergistic effect. This synergistic effect not only increases the conductivity of the composite material, but also enhances the local conductivity difference, thereby optimizing the conductive loss, so that the composite material exhibits good electromagnetic wave absorption performance in a wider frequency range. Among them, the minimum reflection loss reaches -67.93dB, the effective absorption bandwidth is 3.94GHz, and it exhibits excellent wave absorption performance in the Ku band (12-18GHz), which makes the material suitable for stealth materials for shielding radar.

[0017] Application of V2O5 / CNF with a three-dimensional network structure in the field of electromagnetic wave absorption. The application is to mix the V2O5 / CNF with a matrix to prepare an electromagnetic wave absorbing coating or patch. The matrix is polyurea or epoxy resin. The present invention can adjust the complex dielectric constant (ε' and ε") of the composite material by controlling the dosage of the composite nanomaterial, thereby achieving good impedance matching, allowing more electromagnetic waves to enter and be absorbed, and making the minimum reflection loss as high as -67.93dB (thickness is only 1.25mm), thereby improving the absorption efficiency of electromagnetic waves.

[0018] Beneficial effects of the present invention:

[0019] 1. The present application innovatively provides a V2O5-filled carbon nanofiber composite material with a three-dimensional network structure. This structure is significantly different from the carbon fiber composite absorber material reported in the prior art and is also discovered by the inventor for the first time, and has outstanding substantive characteristics.

[0020] 2. The V2O5-filled carbon nanofiber composite material described in this application, based on the aforementioned network structure, achieves a significant improvement in electromagnetic wave absorption performance. It can maintain good electromagnetic wave absorption performance (minimum reflection loss is -67.93dB, effective absorption bandwidth is 3.94GHz) while the material thickness is only 1.25mm (far lower than traditional materials at least 2.5mm), achieving unexpected technical effects.

[0021] 3. The V2O5-filled carbon nanofiber composite material described in this application, based on its excellent electromagnetic wave absorption performance, can greatly reduce the thickness of the material, meet the current demand for lightweight, ultra-thin electromagnetic wave absorption materials, effectively reduce the burden on equipment, meet the requirements of lightweight, and has broad market application prospects. Description of the Drawings

[0022] Attached Figure 1 SEM photograph of V2O5 prepared for Example 1

[0023] Attached Figure 2 SEM photographs of V2O5 / CNF prepared for Example 1 at magnification factors of 4760 times (a) and 20740 times (b)

[0024] Attached Figure 3 Frequency dependence of ε′(a), ε″(b), μ′(d), μ″(e), tanδε(c) and tanδμ(f) for the composite materials prepared for Examples 2 - 4 in the frequency range of 2–18 GHz

[0025] Attached Figure 4 Three - dimensional surface plots of the optimal reflection loss (RL) and A1(a) and (b), A2(c) and (d), A3(e) and (f) for the composite materials prepared for Examples 2 - 4 Detailed Description of the Invention

[0026] The present invention will be further described below in conjunction with the embodiments

[0027] The raw materials used in this embodiment are all obtained through commercial channels. Among them, the polyurea is purchased from Gaodun New Materials Co., Ltd., with the model N - 500. The epoxy resin is purchased from Hangzhou Wuhuigang Adhesive Co., Ltd., with the model E51

[0028] Example 1: Preparation of V2O5 - filled carbon nanofiber composite material with a three - dimensional network structure

[0029] (1) Preparation of the precursor solution: Take an appropriate amount of V2O5 nanoparticles and PANF, stir at 30 °C for 22 h and dissolve in DMF to obtain the precursor solution. Among them, the weight ratio of the V2O5 nanoparticles to PANF is 2:16

[0030] Among them, the V2O5 is prepared by a hydrothermal method, and the specific operation is as follows: First, prepare a mixed solution of 80 mL of ethanol and water (C2H5OH:H2O = 1:9 [v:v]). Then dissolve 0.3 g of NH4VO3 in the mixed solution, denoted as solution A. Ultrasonic for 0.5 h until completely dissolved. Then prepare a 5% hydrochloric acid solution, denoted as solution B. While stirring solution A, add solution B dropwise until the pH is adjusted to 3. Transfer the above solution to a stainless - steel autoclave and react at 140 °C for 20 h. Wash the product three times alternately with ethanol and water and dry overnight at 80 °C to obtain V2O5. Put the dried V2O5 into a mortar and grind it into a powder state, and store it in a dry condition

[0031] (2) Electrospinning: Transfer the precursor solution prepared in step (1) to a spinning device, carry out electrospinning, and collect the product to obtain V2O5 / PANF. Among them, the voltage of the electrospinning is set to 22 kV, and the distance between the needle and the collector is 13 cm.

[0032] (3) Carbonization treatment: After drying and pre-carbonizing the product obtained in step (2), carry out carbonization treatment in an inert gas atmosphere at a temperature of 700 °C for 4 hours to obtain V2O5 / CNF, that is, a V2O5-filled carbon nanofiber composite material with a three-dimensional network structure. Put the product into a mortar and grind it into a powder state, and store it in a dry condition. Among them, the specific drying treatment is: drying at 60 °C for 12 h to obtain dry nanofibers; the specific pre-carbonization is: heating at 300 °C for 1 hour. Among them, both the pre-carbonization step and the carbonization step adopt a uniform heating operation, and the heating rate is 5 °C / min.

[0033] Prepare an electromagnetic wave absorption coating using the V2O5 / CNF composite material prepared above, and detect relevant performance parameters. The specific operation is: mix the V2O5 / CNF with a matrix (total mass is 0.1 g), and use a tablet press to compress and prepare a sample ring with an inner diameter and an outer diameter of 3.04 mm and 7 mm respectively. Among them, the mass ratio of V2O5 / CNF is 50%; the matrix is polyurea.

[0034] Example 2: Preparation of a V2O5-filled carbon nanofiber composite material with a three-dimensional network structure

[0035] Different from Example 1,

[0036] (1) Preparation of the precursor solution: Take an appropriate amount of V2O5 nanoparticles and PANF, stir at 40 °C for 22 h and dissolve them in DMF to obtain the precursor solution. Among them, the weight ratio of the V2O5 nanoparticles to PANF is 3:16.

[0037] (2) Electrospinning: Transfer the precursor solution prepared in step (1) to a spinning device, carry out electrospinning, and collect the product to obtain V2O5 / PANF. Among them, the voltage of the electrospinning is set to 23 kV, and the distance between the needle and the collector is 14 cm.

[0038] (3) Carbonization treatment: After drying and pre-carbonizing the product obtained in step (2), it is carbonized at 800 °C for 3 hours in an inert gas atmosphere to obtain V2O5 / CNF, that is, a V2O5-filled carbon nanofiber composite material with a three-dimensional network structure. The product is put into a mortar and ground into a powder state, and stored in a dry condition. Among them, the drying treatment is specifically: drying at 60 °C for 12 h to obtain dry nanofibers; the pre-carbonization is specifically: heating at 290 °C for 1.5 hours. Among them, both the pre-carbonization step and the carbonization step adopt a uniform heating operation, and the heating rate is 4 °C / min.

[0039] Use the prepared V2O5 / CNF composite material to prepare an electromagnetic wave absorption patch and detect related performance parameters. The specific operation is as follows: Mix the V2O5 / CNF with the matrix (total mass is 0.1 g), and use a tablet press to compress and prepare a sample ring with an inner diameter and an outer diameter of 3.04 mm and 7 mm respectively. Among them, the mass ratio of V2O5 / CNF is 30%. The matrix is polyurea.

[0040] Example 3: Preparation of V2O5-filled carbon nanofiber composite material with a three-dimensional network structure

[0041] Different from Example 1,

[0042] (1) Preparation of precursor solution: Take an appropriate amount of V2O5 nanoparticles and PANF, stir at 50 °C for 21 h and dissolve in DMF to obtain the precursor solution. Among them, the weight ratio of V2O5 nanoparticles to PANF is 3:16.

[0043] (2) Electrospinning: Transfer the precursor solution prepared in step (1) to a spinning device, perform electrospinning, and collect the product to obtain V2O5 / PANF. Among them, the voltage of the electrospinning is set to 24 kV, and the distance between the needle head and the collector is 15 cm.

[0044] (3) Carbonization treatment: After drying and pre-carbonizing the product obtained in step (2), it is carbonized at 800 °C for 3 hours in an inert gas atmosphere to obtain V2O5 / CNF, that is, a V2O5-filled carbon nanofiber composite material with a three-dimensional network structure. The product is put into a mortar and ground into a powder state, and stored in a dry condition. Among them, the drying treatment is specifically: drying at 60 °C for 12 h to obtain dry nanofibers; the pre-carbonization is specifically: heating at 290 °C for 1.5 hours. Among them, both the pre-carbonization step and the carbonization step adopt a uniform heating operation, and the heating rate is 4 °C / min.

[0045] The V2O5 / CNF composite material prepared as described above was used to prepare an electromagnetic wave absorption coating, and relevant performance parameters were measured. The specific operation was as follows: The V2O5 / CNF was mixed with a matrix (total mass was 0.1 g), and a sample ring was prepared by compression using a tablet press. The inner diameter and outer diameter were 3.04 mm and 7 mm respectively. Among them, the mass ratio of V2O5 / CNF was 40%. The matrix was epoxy.

[0046] Example 4: Preparation of V2O5-filled carbon nanofiber composite material with a three-dimensional network structure

[0047] Different from Example 1,

[0048] (1) Preparation of the precursor solution: An appropriate amount of V2O5 nanoparticles and PANF were taken and stirred at 50 °C for 21 h and dissolved in DMF to obtain the precursor solution. Among them, the weight ratio of the V2O5 nanoparticles to PANF was 3:16.

[0049] (2) Electrospinning: The precursor solution prepared in step (1) was transferred to a spinning device for electrospinning, and the product was collected to obtain V2O5 / PANF. Among them, the voltage of the electrospinning was set to 25 kV, and the distance between the needle and the collector was 16 cm.

[0050] (3) Carbonization treatment: The product obtained in step (2) was dried, pre-carbonized, and then carbonized at 900 °C for 2 h in an inert gas atmosphere to obtain V2O5 / CNF, that is, the V2O5-filled carbon nanofiber composite material with a three-dimensional network structure. The product was put into a mortar and ground into a powder state and stored under dry conditions. Among them, the specific drying treatment was: drying at 50 °C for 14 h to obtain dry nanofibers; the specific pre-carbonization was: heating at 280 °C for 2 h. Among them, both the pre-carbonization step and the carbonization step were carried out with a uniform heating operation, and the heating rate was 3 °C / min.

[0051] The V2O5 / CNF composite material prepared as described above was used to prepare an electromagnetic wave absorption patch, and relevant performance parameters were measured. The specific operation was as follows: The V2O5 / CNF was mixed with a matrix (total mass was 0.1 g), and a sample ring was prepared by compression using a tablet press. The inner diameter and outer diameter were 3.04 mm and 7 mm respectively. Among them, the mass ratio of V2O5 / CNF was 50%. The matrix was epoxy.

[0052] Example 5: Preparation of V2O5-filled carbon nanofiber composite material with a three-dimensional network structure

[0053] Different from Example 1,

[0054] (1) Preparation of the precursor solution: Appropriate amounts of V2O5 nanoparticles and PANF were taken and stirred at 60 °C for 20 h in DMF to obtain the precursor solution. Among them, the weight ratio of the V2O5 nanoparticles to PANF was 4:16.

[0055] (2) Electrospinning: The precursor solution prepared in step (1) was transferred to a spinning device for electrospinning, and the product was collected to obtain V2O5 / PANF. Among them, the voltage of the electrospinning was set at 26 kV, and the distance between the needle and the collector was 17 cm.

[0056] (3) Carbonization treatment: The product obtained in step (2) was dried, pre-carbonized, and then carbonized at 900 °C for 2 h in an inert gas atmosphere to obtain V2O5 / CNF, that is, a V2O5-filled carbon nanofiber composite material with a three-dimensional network structure. The product was put into a mortar and ground into a powder state and stored in a dry condition. Among them, the drying treatment was specifically: drying at 50 °C for 14 h to obtain dry nanofibers; the pre-carbonization was specifically: heating at 280 °C for 2 h. Among them, both the pre-carbonization step and the carbonization step were carried out with a uniform heating operation, and the heating rate was 3 °C / min.

[0057] The electromagnetic wave absorption coating machine was prepared using the V2O5 / CNF composite material prepared above, and a sample ring was compressed. The inner diameter and outer diameter were 3.04 mm and 7 mm, respectively. Among them, the mass ratio of V2O5 / CNF was 45%. The matrix was polyurea.

[0058] Comparative Example 1:

[0059] Different from Example 1, V2O5 was not added.

[0060] Comparative Example 2:

[0061] Only the V2O5 prepared by the hydrothermal method was used as the detection object.

[0062] Comparative Example 3:

[0063] Different from Example 1, FeNi nanoparticles were added to replace the V2O5 nanoparticles.

[0064] Example 6: Characterization of the V2O5 nanoparticles and composite materials prepared in Examples 1-5

[0065] (1) Characterization of the morphology by scanning electron microscopy (SEM)

[0066] A scanning electron microscope (Sigma 300, Carl Zeiss) was used to observe the microscopic morphology of the samples (V2O5 nanoparticles and composite materials) prepared in Examples 1-5. SEM uses an electron beam to irradiate the sample surface, and generates a high-resolution surface morphology image by detecting and recording the reflected, scattered or transmitted electron signals. The results are similar, and Example 1 is used as an example for explanation. Figure 1 and Figure 2 .

[0067] Depend on Figure 1 It can be seen that the particle size of V2O5 nanoparticles prepared by the hydrothermal method is about 300-400 nanometers.

[0068] Depend on Figure 2 It can be seen that the V2O5 after electrospinning and the carbon nanofibers formed after high-temperature annealing are cross-linked to form a relatively dense three-dimensional network structure, and the V2O5 is wrapped inside the fiber; specifically: V2O5 is uniformly dispersed in the carbon nanofiber in the form of small-sized particles, and also aggregates into nodes with larger particle sizes, and connects the carbon fibers into a three-dimensional network structure through these nodes. This structure has not been reported in the prior art and is the first discovery of the inventor. Among them, the diameter of the carbon nanofiber is 200-300 nanometers.

[0069] (2) Vector network analyzer (VNA) characterization of electromagnetic parameters of composite materials

[0070] The sample preparation method is as follows: V2O5 / CNF is mixed with paraffin in a corresponding ratio (total mass is 0.1 g), and a sample ring is compressed using a tablet press, with an inner diameter and an outer diameter of 3.04 mm and 7 mm, respectively.

[0071] The electromagnetic parameters of the composite materials prepared in Examples 2-4 were measured by a vector network analyzer (Agilent N5222A) using the coaxial line method in a frequency range of 2.0-18.0 GHz. The results are detailed in Figure 3 VNA is mainly used in the field of radio frequency and electromagnetic waves. It characterizes the electromagnetic parameter information of the circuit or device at the corresponding electromagnetic frequency by measuring the amplitude and phase information between the input signal and the output signal.

[0072] Figure 3 The relative dielectric constants (ε) of the composite materials with three different doping levels prepared in Examples 2-4 are shown in FIG. r ) and relative magnetic permeability (μ r ) are analyzed. The real part (ε′) and imaginary part (ε″) of the dielectric constant, as well as the real part (μ′) and imaginary part (μ″) of the magnetic permeability are analyzed. In addition, the dielectric loss tangent (tanδ ε=(ε″ / ε′)) and magnetic loss tangent (tanδ μ =(μ″ / μ′)) to evaluate the dielectric loss and magnetic loss capabilities. It can be seen from Figure 3 that the real part (ε′) and imaginary part (ε″) of the dielectric constant of the three samples both show a downward trend with the increase of the test frequency and an upward trend with the increase of the doping level, which can be explained by the free electron theory. In addition, many resonance peaks appear on the curve, indicating the existence of multiple polarizations, such as dipolar polarization and interfacial polarization. As shown in Figure 3 (c), the dielectric loss generally increases with the increase of the material dosage. As shown in Figure 3 (d) to (e), there is no obvious difference in the magnetic permeability of materials with different contents. This is because the magnetism of the material is relatively weak and does not improve significantly with the increase of the content. Figure 3 (f) shows that the magnetic loss is very small, significantly lower than the dielectric loss, indicating that the dielectric loss dominates.

[0073] By further calculating the Figure 3 data, the electromagnetic wave absorption and properties of the material are obtained. The results are shown in detail in Figure 4 and Table 1. The electromagnetic wave absorption performance described is the best absorption performance of the detection object. Therefore, the matching thickness and bandwidth of different detection samples are different.

[0074] Figure 4 shows the electromagnetic wave absorption performance of three different doping level materials prepared in Examples 2-4. When RL is less than -10 dB, it indicates that 90% of the electromagnetic waves are effectively absorbed. It can be seen from Figure 4 that for the composite material prepared in Example 2, when the doping level is 30%, the minimum reflection loss is -36.61 dB at 14.16 GHz, the matching thickness is 5.2 mm, and the effective absorption bandwidth is 1.76 GHz. For the composite material prepared in Example 3, when the doping level is 40%, the minimum reflection loss is -41.94 dB, the matching thickness is 2.45 mm, and the effective absorption bandwidth is 2.26 GHz. For the composite material prepared in Example 4, when the doping level is 50%, the minimum reflection loss reaches -67.93 dB, the matching thickness is only 1.25 mm, and the effective absorption bandwidth is 3.94 GHz. It can be seen from Table 1 that for the composite material prepared in Example 1, when the doping level is 50%, the minimum reflection loss reaches -52.68 dB, the matching thickness is only 2.15 mm, and the effective absorption bandwidth is 2.58 GHz; for the composite material prepared in Example 5, when the doping level is 45%, the minimum reflection loss reaches -59.57 dB, the matching thickness is only 2.30 mm, and the effective absorption bandwidth is 2.44 GHz.

[0075] In summary, for the coatings or patches prepared from the composite material of V2O5 / CNF, when the matching thickness is 1.25 - 5.20 mm, the minimum RL reaches -36.61 to -67.93 dB, and the effective bandwidth is 1.76 to 3.94 GHz. This indicates that the V2O5 / CNF composite material not only has a three-dimensional network structure, which has prominent substantial features compared with the prior art, but also has excellent electromagnetic wave absorption performance, resulting in significant progress. The inventor speculates that this is because: First, the network structure of V2O5 / CNF enables good impedance matching and allows electromagnetic waves to be reflected and attenuated multiple times therein, improving the absorption efficiency. Second, the free carriers in V2O5 generate current under the action of the electromagnetic field, converting electromagnetic energy into heat energy for conduction loss. Finally, the dipoles in V2O5 (such as lattice defects and interfacial polarization) undergo relaxation, promoting energy loss. Charge accumulation occurs at the interface between V2O5 and CNF to form interfacial polarization, promoting dielectric loss.

[0076] Table 1 Electromagnetic parameters of the composite materials prepared in Examples 1 - 5

[0077] Number Dosage (%) Minimum RL (dB) Matching thickness (mm) Effective bandwidth (GHz) Example 1 50 -52.68 2.15 2.58 Example 2 30 -36.61 5.20 1.76 Example 3 40 -41.94 2.45 2.26 Example 4 50 -67.93 1.25 3.94 Example 5 45 -59.57 2.30 2.44

[0078] Table 2 Electromagnetic parameters of the materials prepared in Comparative Examples 1 - 3

[0079] Number Dosage (%) Minimum RL (dB) Matching thickness (mm) Effective bandwidth (GHz) Comparative example 1 50 -35.35 3.50 3.48 Comparative example 2 50 -9.58 5.60 --- Comparative example 3 50 -57.85 2.77 3.79

[0080] As can be seen from Table 2, Comparative Example 1 is pure CNF without adding V2O5. At a doping content of 50%, with a matching thickness of 3.50 mm, the minimum RL is -35.35 dB, and the effective bandwidth is 3.48 GHz. Comparative Example 2 is pure V2O5. At a doping content of 50%, with a matching thickness of 5.60 mm, the minimum RL is -9.58 dB, and there is no effective bandwidth. From the results of Example 1 and Example 2, it can be seen that the minimum reflection loss RL of the V2O5 / CNF composite material prepared in this application is significantly higher than the simple superposition of pure CNF and pure V2O5 alone, achieving a technical effect of 1+1>2, which meets the requirements of the patent law regarding creativity. The inventor speculates that this is closely related to its unique three-dimensional structure. In addition, Comparative Example 3 is a CNF composite material using FeNi to replace V2O5. At a doping content of 50%, with a matching thickness of 2.77 mm, the minimum RL is -57.85 dB, and the effective bandwidth is 3.79 GHz. For the composite material prepared in Example 4, when the doping content is 50%, the minimum reflection loss reaches -67.93 dB, the matching thickness is only 1.25 mm, and the effective absorption bandwidth is 3.94 GHz, which is significantly better than Comparative Example 3. This shows that its electromagnetic wave absorption performance achieves more excellent electromagnetic wave absorption performance under the condition of lower material thickness compared with the prior art, achieving an unexpected technical effect.

[0081] In summary, this application reports for the first time the preparation of a composite material with a three-dimensional network structure by electrospinning V2O5; the composite material provides a lower density and more scattering paths, and due to the interfacial polarization and dielectric loss between V2O5 and CNF, the prepared V2O5 / CNF composite material has good electromagnetic wave absorption performance, achieving an unexpected technical effect. Based on this, the V2O5-filled carbon nanofiber composite material described in this application greatly reduces the thickness of the material, meets the current requirements for lightweight and ultra-thin electromagnetic wave absorption materials, effectively reduces the burden on equipment, meets the requirements of lightweight, and has broad application prospects.

Claims

1. A V2O5-filled carbon nanofiber composite with a three-dimensional network structure, characterized in that: The composite material includes a three-dimensional skeleton composed of carbon nanofibers and V2O5 nanoparticles dispersed in the three-dimensional skeleton in an embedded form.

2. The V2O5-filled carbon nanofiber composite according to claim 1, characterized in that: The diameter of the carbon nanofibers is 200 - 300 nanometers, and the particle size of the V2O5 nanoparticles is 300 - 400 nanometers.

3. The preparation method of the V2O5-filled carbon nanofiber composite material according to claim 1 or 2, characterized in that: It includes the following steps: (1) Preparation of the precursor solution: Take an appropriate amount of V2O5 nanoparticles and PANF, dissolve them in DMF to obtain the precursor solution. (2) Electrospinning: Transfer the precursor solution prepared in step (1) to a spinning device, perform electrospinning, and collect the product to obtain V2O5 / PANF; (3) Carbonization treatment: Dry and pre-carbonize the product obtained in step (2), and then perform carbonization treatment in an inert gas atmosphere at a temperature of 700°C - 900°C for 2 - 4 hours to obtain V2O5 / CNF, that is, a V2O5-filled carbon nanofiber composite material with a three-dimensional network structure.

4. The preparation method of the V2O5-filled carbon nanofiber composite according to claim 3, characterized in that: In step (1), the weight ratio of the V2O5 nanoparticles to PANF is 2:16 - 4:

16.

5. The preparation method of the V2O5-filled carbon nanofiber composite according to claim 4, characterized in that: The specific operation for preparing the precursor in step (1) is to stir at 30 - 60°C for 20 - 22 h; the voltage for electrospinning in step (2) is set at 22 - 26 kV, and the distance between the needle and the collector is 13 - 17 cm.

6. The preparation method of the V2O5-filled carbon nanofiber composite material according to claim 4, characterized in that: The specific drying treatment in step (3) is: drying at 50 - 60°C for 12 - 14 h to obtain dry nanofibers; the specific pre-carbonization is: heating at 280 - 300°C for 1 - 2 hours.

7. The preparation method of the V2O5-filled carbon nanofiber composite material according to any one of claims 3-6, characterized in that: Both the pre-carbonization step and the carbonization step are carried out with a uniform temperature increase operation, and the heating rate is 3 - 5°C / min.

8. Application of V2O5 / CNF with a three-dimensional network structure in the field of electromagnetic wave absorption.

9. The application according to claim 8, characterized in that: The application is to mix the V2O5 / CNF with a matrix to prepare an electromagnetic wave absorption coating or patch.

10. The application according to claim 9, characterized in that: The matrix is polyurea or epoxy resin.

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