A Fe3O4 / multi-walled carbon nanotube composite wave-absorbing filler and its preparation method and application

Abstract

The present invention belongs to the technical field of material preparation, and specifically relates to a Fe3O4 / multi-walled carbon nanotube composite absorbing filler, and its preparation method and application. The present invention blends carbon nanotubes with magnetic fillers, and chitosan added during the synthesis of the composite filler can play a role of "adhesion", building a "bridge" between Fe3O4 microspheres and MWCNTs, and realizing the construction of a spatially ordered morphology between the magnetic microspheres and the conductive carbon tubes, and ultimately achieving the adjustment of the electromagnetic properties of the absorbing filler by regulating the microscopic morphology, and establishing a structure and performance regulation scheme. The composite of the two fillers not only improves the dispersibility of the carbon nanotubes, but the Fe3O4 nanoparticles also provide effective hysteresis loss, thereby improving the electromagnetic wave absorption performance; and the effective composite lightness of the two fillers improves the problem of heavy weight of densely stacked materials and easy deposition during the application of coating materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of material preparation, and in particular relates to a Fe3O4 / multi-walled carbon nanotube composite wave-absorbing filler and a preparation method and application thereof. Background Art

[0002] In modern warfare, countries around the world prioritize improving the survivability, penetration, and deep strike capabilities of weapons and equipment. However, with the rapid advancement of detection technology and precision-guided weapons, the detection of weapons and equipment by detection systems can have fatal consequences. To improve the concealment capabilities of military weapons and equipment and aircraft, stealth technology has become a key solution. Stealth technology refers to the ability to evade radar and other detection methods within a small range. However, the key to stealth lies in absorbing materials. Absorbing materials can be categorized as either coated or structured. Coated absorbers offer advantages such as simple preparation processes and low cost. Therefore, using absorbing coatings can impart radar stealth to aircraft. In absorbing coatings, electromagnetic wave absorbers and fillers contribute significantly to losses, making the research of new, highly efficient absorbers a key and challenging task.

[0003] According to the different mechanisms, absorbers can be divided into electric loss type absorbers and magnetic loss type absorbers. However, it is difficult for a single type of absorber to achieve the ideal absorbent effect. Therefore, the electric loss type absorber and the magnetic loss type absorber are combined, and the two different absorbent mechanisms are combined to improve the absorbent performance of the composite material to prepare MWCNTs / Fe3O4 composite absorbent fillers. Fe3O4 is the main component of magnetite, belongs to the cubic crystal system, and has an inverse spinel structure. In the Fe3O4 crystal, oxygen atoms are densely packed in cubic form, and iron atoms occupy the gaps between tetrahedrons and octahedrons. Among them, Fe 3+ Occupies the tetrahedral gaps, while the octahedral gaps are occupied by Fe 2+ and Fe 3+ Average occupation. Based on this special crystal structure, Fe3O4 has both magnetic loss and dielectric loss for electromagnetic waves, thus showing good electromagnetic wave absorption performance in certain specific frequency bands. Compared with ordinary magnetite, Fe3O4 nanoparticles have shown many excellent characteristics. Such as large specific surface area, high magnetic strength and good paramagnetism. MWCNTs are tubular structures formed by curling multiple layers of graphite and have unique electrical properties. The production cost is low, it is easy to mass produce and has high chemical stability. Therefore, MWCNTs are widely used in the field of electromagnetic shielding. The carbon atoms in carbon nanotubes are sp 2Hybrid materials are primarily characterized by high conductivity, light weight, an extremely high aspect ratio, and great mechanical strength. Their application in polymer-based electromagnetic shielding materials offers significant advantages, achieving high electromagnetic shielding effectiveness even with relatively low content in the polymer matrix. However, when these two materials are used alone as absorbing fillers, it is difficult to achieve the current comprehensive performance targets for absorbing fillers. This is because the single-component Fe₃O₄ has a relatively high density, and single-component MWCNTs require complex surface modification to improve their dispersibility in the polymer matrix. Furthermore, their narrow absorption band limits their large-scale industrial application.

[0004] CN 102350282 A discloses a method for preparing a cobalt-nickel ferrite / multi-walled carbon nanotube magnetic nanocomposite material. The nanocomposite material obtained by acidifying MWCNTs is highly dispersible and not prone to agglomeration. However, the acidification of MWCNTs requires a highly oxidizing concentrated acid, and the acidification time is long, which is not conducive to industrial production. CN 101320607B discloses a method for preparing a Fe3O4 / MWCNTs magnetic nanocomposite material using an alcohol-thermal method. The MWCNTs are acidified to enhance the binding effect with Fe3O4. Although Fe3O4 can adhere to the MWCNT surface, the binding stability is poor. The chitosan added to the system in this case is not only non-toxic and harmless, but also acts as a "bridging" agent, allowing Fe3O4 to be tightly wrapped around the MWCNT surface, forming a stable three-dimensional network structure. CN 103435972 A relates to a method for preparing a nickel-zinc-ferrite-multi-walled carbon nanotube-epoxy resin composite material. The method requires using a strong acid to acidify the multi-walled carbon nanotubes for a long time to achieve the modification purpose. Furthermore, the separation and purification process of the nickel-zinc-iron / MWCNTs composite powder is complex and requires the use of toxic reagents, making it unsuitable for large-scale environmentally friendly production.

[0005] Therefore, how to provide a Fe3O4 / multi-walled carbon nanotube composite absorbing filler that is lightweight, structurally stable, has high-efficiency absorbing performance, and has a green production process is a technical problem that needs to be urgently solved by those skilled in the art. Summary of the Invention

[0006] In view of this, in order to solve the problems of high toxicity, poor binding effect and unfavorable industrial production of the used agents, the present invention discloses a Fe3O4 / multi-walled carbon nanotube composite absorbing filler and a preparation method thereof. The filler is a MWCNTs / Fe3O4 composite absorbing filler containing both an electrical loss type absorbing material and a magnetic loss type absorbing material.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] The first technical purpose of the present invention is to provide a method for preparing a Fe3O4 / multi-walled carbon nanotube composite absorbing filler, the method specifically comprising the following steps:

[0009] ① Add ethylene glycol, FeCl3·6H2O, MWCNTs and chitosan to a three-necked glass flask equipped with an ultrasonic and stirring device, stir ultrasonically at room temperature, and start the reaction timer;

[0010] ② After the timed reaction in step ① is completed, polypropylene glycol 2000 (PPG2000) and sodium acetate (NaAc) are added to the system and ultrasonic stirring is continued to start the timed reaction;

[0011] ③ After the timed reaction in step ② is completed, the reaction solution is transferred into the polytetrafluoroethylene lining of the reactor and placed in a box-type atmosphere furnace for thermal reaction timed treatment;

[0012] ④ After the thermal reaction timer treatment in step ③ is completed, cool to room temperature (25°C) and pour into a beaker and let it stand. After standing and stratification, pour out the supernatant and repeatedly wash with anhydrous ethanol and deionized water to remove impurities;

[0013] ⑤Separate the product by suction filtration or filtration;

[0014] ⑥ Place the filter cake from step ⑤ in a vacuum drying oven for drying and removing water to obtain the target product MWCNTs / Fe3O4 composite absorbing material.

[0015] Optionally, the method further comprises removing water from the raw materials: drying FeCl3·6H2O, MWCNTs, sodium acetate (NaAc) and chitosan under vacuum conditions at 70-90°C for 2-3 hours to remove water from the solid raw materials.

[0016] Furthermore, the raw material dehydration is carried out in a vacuum drying oven, the vacuum drying temperature is 70-90° C., the vacuum pressure is -0.08 to -0.10 MPa, and the drying time is 2-3 hours.

[0017] Optionally, in step ①, the order of adding ethylene glycol, FeCl3·6H2O, MWCNTs and chitosan is to first add 140 ml of ethylene glycol, then add the ground FeCl3·6H2O powder and MWCNTs, and finally add chitosan powder, and react with ultrasonic stirring for 1-1.5 hours.

[0018] Optionally, in step ⑤, the product is separated by suction filtration or filtration, and the product is washed with anhydrous ethanol 3-5 times to remove PPG2000 in the product, and then washed with pure water.

[0019] Optionally, in step ③, the vacuum drying temperature is 160-190° C., the vacuum pressure is -0.08 to -0.10 MPa, and the drying time is 10-12 h.

[0020] Optionally, in step ⑥, the vacuum drying temperature is 70-90° C., the vacuum pressure is -0.08 to -0.10 MPa, and the drying time is 1-2 h.

[0021] Optionally, the reaction time in step ② is 0.5-1h.

[0022] It should be noted that MWCNTs are characterized by their light weight, large specific surface area, and excellent electrical and thermal conductivity. Furthermore, even at relatively low concentrations within a polymer matrix, they can achieve high electromagnetic shielding effectiveness. However, from the perspective of absorbing filler design, simply adding carbon nanotubes to a resin matrix cannot achieve good dispersion and lacks magnetic properties, which limits further improvement in their absorbing performance. Furthermore, single-component Fe₃O₄ nanoparticles also struggle to meet the comprehensive performance targets currently considered for electromagnetic shielding materials. To improve the absorbing performance of single-component MWCNTs and Fe₃O₄ particles, the two were combined to leverage their synergistic effect to enhance the electromagnetic wave absorption performance of the polymer composite.

[0023] In order to improve the absorbing performance of polymer-based absorbing composite materials, there are mainly the following methods: 1) Adjust the content of electric loss type absorber or magnetic loss type absorber in the resin matrix. 2) Fill two or more absorbing materials of the same loss type. 3) Compound two or more absorbing materials of different loss types. The existing methods have the following problems: 1) Using a single loss type or a single type of absorbing material may increase the weight of the absorbing composite material and make it difficult to achieve the ideal absorbing effect. 2) Filling two or more absorbing materials of the same loss type can increase the effective absorption bandwidth to a certain extent and improve the absorbing effect. However, it is difficult to improve the problem of high density and heavy weight of some magnetic loss absorbers. 3) Compounding two or more absorbing materials of different loss types can make the composite material have both electric loss and magnetic loss for electromagnetic waves, such as compounding carbon material (electric loss type absorbing material) and ferromagnetic material (magnetic loss absorbing material).

[0024] However, existing methods do not achieve a simple, environmentally friendly, and effective composite process. Highly corrosive reagents are used during the composite process, and some handling procedures are cumbersome. Furthermore, the composite may experience a "1+1<2" situation, where the two materials may damage each other's structures, inhibit grain growth, and fail to achieve ideal adhesion or overlap. Furthermore, composite fillers prepared using existing methods have not been widely used in the field of electromagnetic wave absorption.

[0025] This invention blends carbon nanotubes with magnetic fillers. The chitosan added during the composite filler synthesis acts as a "bonding agent," building a "bridge" between the Fe₃O₄ microspheres and the MWCNTs. This creates a spatially ordered morphology between the magnetic microspheres and the conductive carbon tubes. Ultimately, the electromagnetic properties of the absorbing filler are adjusted by manipulating the microscopic morphology, establishing a structure and performance control scheme. The combination of the two fillers not only improves the dispersion of the carbon nanotubes, but also provides effective hysteresis loss from the Fe₃O₄ nanoparticles, further enhancing electromagnetic wave absorption performance. Furthermore, the lightweight nature of the effective composite reduces the heavy weight of densely packed materials and their tendency to sediment during coating applications.

[0026] The second technical purpose of the present invention is to provide a Fe3O4 / multi-walled carbon nanotube composite absorbing filler prepared by the method described above.

[0027] The third technical purpose of the present invention is to provide an application of the Fe3O4 / multi-walled carbon nanotube composite absorbing filler prepared by the method as described above in military weapons and equipment.

[0028] Specifically, the Fe3O4 / multi-walled carbon nanotube composite absorbing filler prepared according to the above method is used in the stealth of fighter jets and ships.

[0029] Furthermore, the Fe3O4 / multi-walled carbon nanotube composite absorbing filler is used in absorbing coatings.

[0030] With the rapid development of detection technology, weapons and equipment are facing more demanding service conditions, and the requirements for "thin, light, wide, and strong" absorbing coatings are also being put forward. MWCNTs / Fe3O4 composite absorbing fillers have excellent absorption properties while facilitating the lightweight design of absorbing materials, which can meet the above requirements. On the one hand, the composite of Fe3O4 nanoparticles and MWCNTs can obtain the characteristics of both components, thereby improving their overall performance. On the other hand, the "collision" and composite of the two components can create some new structures, interfaces, and bridges, which are conducive to the absorption of electromagnetic waves. In addition, by adjusting the content of MWCNTs, the electromagnetic parameters of the absorbing filler can be effectively adjusted, and thus the absorbing performance of the absorbing coating can be adjusted.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1) The present invention discloses a simple one-step solvothermal method for preparing MWCNTs / Fe3O4 nanocomposite fillers, and the process is simple and is conducive to mass preparation and production.

[0033] 2) The nanocomposite filler forms a unique three-dimensional network structure. In the MWCNTs / Fe3O4 nanocomposite filler, the Fe3O4 nanoparticles and MWCNTs are composited relatively uniformly without agglomeration. The interface and bridging structures at the connection between the two can better assist the material in absorbing electromagnetic waves.

[0034] 3) The microwave absorption performance of pure MWCNTs samples, pure Fe3O4 samples and their simple physical blends is not ideal, while the structure of the junction of MWCNTs and Fe3O4 nanocrystals synthesized by the method of the present invention has a strong interaction, and the charge can be easily transferred from Fe3O4 to MWCNTs through the junction. The hybrid structure of the two is conducive to the dipole interaction of the composite material, thereby improving the microwave absorption performance of the composite material.

[0035] 4) This invention meets the requirement for new microwave-absorbing materials to be lightweight. MWCNTs have a low density, which facilitates the lightweighting of microwave-absorbing composite materials and provides a method for preparing lightweight microwave-absorbing coatings.

[0036] 5) The present invention can effectively adjust the complex dielectric constant of the MWCNTs / Fe3O4 nanocomposite material by adjusting the content of MWCNTs, and further effectively adjust the absorbing performance of the absorbing coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0038] Figure 1 Scanning electron microscope images of MWCNTs / Fe3O4 composite absorbing materials prepared in (a) Example 1, (b) Example 2, and (c) Example 3.

[0039] Figure 2 This is the EDS surface scanning energy spectrum of the MWCNTs / Fe3O4 composite absorbing material prepared in Example 3, including C, Fe and O elements.

[0040] Figure 3 1 is the infrared spectrum of the MWCNTs / Fe3O4 composite absorbing material prepared in Examples 1, 2, and 3.

[0041] Figure 4 3 is a graph comparing the electromagnetic parameters of the MWCNTs / Fe3O4 composite absorbing materials prepared in Example 1 and Example 3.

[0042] Figure 5 This is a reflection loss diagram of the MWCNTs / Fe3O4 composite absorbing material prepared in Example 3 (5 mm). DETAILED DESCRIPTION

[0043] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0044] The term "embodiment" is used herein specifically to describe any embodiment as "exemplary," and should not be construed as superior or preferable to other embodiments. Performance indicators in the embodiments of this application were tested using conventional testing methods in the art, unless otherwise specified. It should be understood that the terms used in this application are intended solely to describe specific implementations and are not intended to limit the disclosure herein.

[0045] Unless otherwise specified, the technical and scientific terms used herein have the same meanings as commonly understood by ordinary technicians in the technical field to which this application belongs; other experimental methods and technical means not specifically specified in this application refer to experimental methods and technical means commonly used by ordinary technicians in this field.

[0046] In order to better illustrate the content of this application, numerous specific details are provided in the specific examples below. It should be understood by those skilled in the art that this application can be implemented without certain specific details. In the examples, some methods, means, instruments, equipment, etc. well known to those skilled in the art are not described in detail in order to highlight the main purpose of this application.

[0047] Under the premise of no conflict, the technical features disclosed in the embodiments of this application can be combined arbitrarily, and the resulting technical solutions belong to the contents disclosed in the embodiments of this application.

[0048] The invention discloses a Fe3O4 / multi-walled carbon nanotube composite wave absorbing filler and a preparation method thereof

[0049] For a better understanding of the present invention, the present invention is further specifically described below through the following examples, but it should not be understood as limiting the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above invention content are also considered to fall within the scope of protection of the present invention.

[0050] Examples 1-3

[0051] Examples 1-3 of the present invention disclose the preparation technology of Fe3O4 and MWCNTs / Fe3O4, which includes the following steps:

[0052] ① Dry FeCl3·6H2O, MWCNTs, NaAc and chitosan at 80℃ under vacuum for 2-3 hours to remove moisture from the solid raw materials;

[0053] ② First, add 140 mL of ethylene glycol to a 250 mL three-necked flask, and then add FeCl3·6H2O, MWCNTs, and chitosan to the three-necked flask in sequence;

[0054] ③Ultrasonic stirring at room temperature for 1 h;

[0055] ④ After the timed reaction is completed, PPG2000 and NaAc are added to the three-necked flask and ultrasonic stirring is continued for 0.5 h;

[0056] ⑤ After the timed reaction is completed, turn off the ultrasound and stirring, transfer the reaction solution into the polytetrafluoroethylene liner of the reactor, and place it in a vacuum drying oven. The vacuum drying temperature is 180°C, the vacuum pressure is -0.08 to -0.10 MPa, and the drying time is 12 hours;

[0057] ⑥ After the timed reaction is completed, the product is poured out and allowed to stand after cooling to room temperature, and then washed several times with anhydrous ethanol and deionized water to remove impurities;

[0058] ⑦Separate the product by filtration;

[0059] ⑧Put the filter cake into a vacuum drying oven for drying and dehydration. The vacuum drying temperature is 80°C, the vacuum pressure is -0.08 to -0.10 MPa, and the drying time is 1 h to obtain the target product MWCNTs / Fe3O4 composite absorbing material.

[0060] Comparative Example 1-2 was used to verify the example from two aspects: whether MWCNTs were added or not and whether chitosan was added or not.

[0061] The raw material ratios and preparation conditions in Examples 1-3 and Comparative Examples 1-2 are shown in Table 1.

[0062] Table 1 Raw material ratios and preparation conditions of Examples 1-3 and Comparative Examples 1-2

[0063]

[0064] To further demonstrate the beneficial effects of the present invention and to provide a better understanding of the present invention, the following experimental examples are provided to further illustrate the technical features disclosed in the present invention, but are not to be construed as limiting the present invention. Other improvements made by those skilled in the art based on the above invention without inventive work are also deemed to fall within the scope of protection of the present invention.

[0065] Comparative Example 1 is a preparation of pure Fe3O4 without MWCNTs and chitosan. In this preparation process, after ultrasonic stirring, the reaction solution is yellow-brown. After being placed in a reactor for high-temperature reaction and washed and dried, the final product is a reddish-brown powder.

[0066] Comparative Example 2 is a preparation of Fe3O4 containing chitosan but not MWCNTs. In this preparation process, after ultrasonic stirring, the reaction solution is yellow-brown. After being placed in a reactor for high-temperature reaction and washed and dried, the final product is a black powder.

[0067] Examples 1, 2, and 3 are MWCNTs / Fe3O4 composite absorbers prepared with different MWCNTs content ratios. After ultrasonic stirring during the preparation process, all three reaction solutions were dark green. After being placed in a reactor for high-temperature reaction and washed and dried, the final products were all black powders. The SEM (scanning electron microscope) images of the samples show that in the resulting composite absorber, the Fe3O4 microspheres are regular spherical and densely loaded and accumulated on the surface of the CNTs. Measurements show that the diameter of the microspheres is approximately between 160 and 267 nm, with a small particle size and a large specific surface area. At the same time, it can be found that some spherical particles are wrapped around the CNTs in a "sugar-coated haws string"-like manner, forming a stable three-dimensional network structure. No free Fe3O4 nanoparticles were observed in the samples. The above analysis shows that the Fe3O4 nanoparticles were successfully loaded on the surface of the MWCNTs.

[0068] Moreover, if Figure 2 As shown, in the EDS spectrum of the MWCNTs / Fe3O4 composite absorbing material prepared in Example 3, the nitrogen element is evenly distributed in the composite absorbing material, proving that chitosan is evenly distributed in the MWCNTs / Fe3O4 composite absorbing material.

[0069] according to Figure 4 As can be seen from (ab), the electromagnetic parameters of the samples prepared in Example 3 and Comparative Example 1 make the test results significantly different. The ε' of Example 3 increases from 4.64-9.97 to 8.27-16.51, and ε" increases from 1.56-2.69 to 2.12-4.8, indicating that the introduction of MWCNTs can significantly improve the dielectric loss of the composite filler. Figure 4(cd) It can be seen that due to the addition of MWCNTs, the real part of the complex magnetic permeability increases in most frequency bands, while the imaginary part of the complex magnetic permeability decreases relatively in most frequency bands. μ" increases from -0.29 to -0.05 to -0.06 to 0.046 in the range of 13.41-18 GHz, indicating that the addition of non-magnetic MWCNTs will reduce the magnetic loss performance of Fe3O4. However, in the Ku band (12 GHz-18 GHz), the magnetic loss increases. This is mainly due to the interfacial polarization between Fe3O4 nanoparticles and the interfacial polarization between MWCNTs and Fe3O4, which can cause the magnetic enhancement of the composite system. This shows that MWCNTs and Fe3O4 nanoparticles can improve the magnetic loss characteristics of the composite filler through synergistic enhancement, which is beneficial to the improvement of the wave absorption characteristics.

[0070] In summary, the addition of MWCNTs increases the imaginary part of the complex dielectric constant of the composite absorbing filler, and the dielectric loss of the composite filler increases accordingly, providing a good electrical loss foundation for the composite filler's microwave absorption properties. Fe₃O₄ nanoparticles contribute to the composite filler's magnetic loss, and the "bridging" effect of chitosan enhances the interfacial polarization between MWCNTs and Fe₃O₄. In the Ku band, this enhanced interfacial polarization further increases the composite filler's magnetic loss, providing a good magnetic loss foundation for the composite filler's microwave absorption properties. Therefore, the chitosan-containing MWCNTs / Fe₃O₄ composite filler prepared in the present invention possesses the structural foundation for exhibiting excellent microwave absorption properties.

[0071] The reflection loss test results can reflect the material's wave-absorbing properties. The lower the reflection loss value, the higher the test sample's absorption of electromagnetic waves. The reflection loss frequency can be used to evaluate the application of absorbing materials. Wave-absorbing fillers with outstanding wave-absorbing properties in the X-band and Ku-band (12GHz-18GHz) frequency ranges are mainly used in stealth coating materials. The reflection loss spectrum shows that Example 3 has a reflection loss of less than -10dB in the 3.96-5.43GHz and 13.8-15.84GHz frequency bands, and the reflection loss bandwidth below -10dB is 3.51GHz. This indicates that the composite filler has a high degree of electromagnetic wave absorption over a wide frequency range (absorption can reach >90%). Therefore, this wave-absorbing filler is expected to be used in stealth coating materials for fighter jets and ships.

[0072] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing Fe3O4 / multi-walled carbon nanotube composite absorbing filler, characterized in that: The method specifically comprises the following steps: ① Stir ethylene glycol, FeCl3·6H2O, MWCNTs, and chitosan under ultrasonic conditions at room temperature and start the reaction timer; ② After the timed reaction in step ① is completed, polypropylene glycol 2000 (PPG2000) and sodium acetate (NaAc) are added to the system and ultrasonic stirring is continued to start the timed reaction; ③ After the timing reaction in step ② is completed, the reaction solution is transferred into the polytetrafluoroethylene liner of the reaction kettle and placed in a box-type atmosphere furnace for vacuum drying and reaction timing treatment; ④ After the vacuum drying reaction timer treatment in step ③ is completed, cool to room temperature 25°C and let it stand. After standing and stratification, pour out the supernatant and repeatedly wash with anhydrous ethanol and deionized water to remove impurities; ⑤ Separate the product by suction or filtration; ⑥ The filter cake obtained in step ⑤ was vacuum dried to remove water to obtain the target product MWCNTs / Fe3O4 composite absorbing material.

2. The method for preparing the Fe3O4 / multi-walled carbon nanotube composite wave absorbing filler according to claim 1, characterized in that: The method further comprises removing water from the raw materials: placing FeCl3·6H2O, MWCNTs, sodium acetate (NaAc) and chitosan under vacuum conditions at 70-90°C for 2-3 hours to remove water from the solid raw materials.

3. The method for preparing the Fe3O4 / multi-walled carbon nanotube composite wave absorbing filler according to claim 2, characterized in that: The raw material dehydration is carried out in a vacuum drying oven, the vacuum drying temperature is 70-90°C, the vacuum pressure is -0.08 to -0.10 Mpa, and the drying time is 2-3 hours.

4. The method for preparing the Fe3O4 / multi-walled carbon nanotube composite wave absorbing filler according to claim 1, characterized in that: In step ①, the order of adding ethylene glycol, FeCl3·6H2O, MWCNTs and chitosan is to first add 140 ml of ethylene glycol, then add the ground FeCl3·6H2O powder and MWCNTs, and finally add chitosan powder, and react with ultrasonic stirring for 1-1.5 h.

5. The method for preparing the Fe3O4 / multi-walled carbon nanotube composite wave absorbing filler according to claim 1, characterized in that: In step ③, the vacuum drying temperature is 160-190° C., the vacuum pressure is -0.08 to -0.10 MPa, and the drying time is 10-12 h.

6. The method for preparing the Fe3O4 / multi-walled carbon nanotube composite wave absorbing filler according to claim 1, characterized in that: In step ⑤, the product is separated by suction filtration or filtration, and the product is washed with anhydrous ethanol 3-5 times to remove PPG2000 in the product, and then washed with pure water.

7. The method for preparing the Fe3O4 / multi-walled carbon nanotube composite wave absorbing filler according to claim 1, characterized in that: In step ⑥, the vacuum drying temperature is 70-90° C., the vacuum pressure is -0.08 to -0.10 MPa, and the drying time is 1-2 h.

8. The method for preparing the Fe3O4 / multi-walled carbon nanotube composite wave absorbing filler according to claim 1, characterized in that: The reaction time in step ② is 0.5-1h.

9. A Fe3O4 / multi-walled carbon nanotube composite absorbing filler prepared by the method of claim 1.

10. Use of the Fe3O4 / multi-walled carbon nanotube composite absorbing filler prepared by the method of claim 1 in military weapons and equipment.

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