A Co9S8-carbon fiber composite microwave absorbing material, its preparation method and application

Abstract

The application belongs to the technical field of microwave absorbing materials, and specifically designs a Co9S8-carbon fiber composite wave-absorbing material, a preparation method and application thereof. The composite wave-absorbing material comprises two parts of hollow Co9S8 and carbon fiber. Sulfacetaide is introduced into a precursor of ZIF-67 as a sulfur source to etch ZIF-67, so as to form a hollow structure Co3S4 / ZIF-67 composite, which is then introduced into polyacrylonitrile nanofiber, and then high-temperature carbonization is carried out to obtain a Co9S8-carbon fiber composite with adjustable dielectric and magnetic properties. The prepared composite material solves the problem of impedance mismatch caused by the lack of multiple loss mechanism synergy of single carbon material and single MOF derived material, and the light carbon fiber composite material has potential application prospect in the fields of aviation, aerospace and the like.

Description

Technical Field

[0001] This invention belongs to the field of microwave absorbing materials technology, specifically relating to a Co9S8-carbon fiber composite microwave absorbing material, its preparation method, and its application. Background Technology

[0002] Against the backdrop of advancements in 5G electronic communication equipment and aerospace technology, the demand for electromagnetic absorbing materials has surged significantly due to the urgent need to mitigate electromagnetic radiation-related pollution. In this context, one of the biggest challenges remains obtaining lightweight materials with high microwave absorption properties. Carbon fiber, due to its remarkable combination of lightweight, high strength, and fatigue resistance, has become an essential component in aircraft and rocket construction. Its application in effectively absorbing radar waves to enable stealth in military aircraft is particularly noteworthy. However, it is important to note that the relatively high dielectric constant of carbon fiber often leads to a significant impedance mismatch with free space.

[0003] Researchers have employed various methods to tune the impedance matching of carbon fibers, such as surface modification, low-temperature carbonization, porous structure design, and the formation of heterojunctions with other materials. Metal sulfides possess inherent conductivity and magnetism, offering promising prospects for microwave absorption. When combined with carbon fibers, they can achieve electromagnetic synergy, and the hierarchical, non-homogeneous phase structure induces interfacial polarization to optimize impedance matching, thus attracting widespread attention in the microwave absorption field. Researchers have described the significant potential of various metal sulfides. To optimize microwave absorption performance, researchers have adopted innovative design strategies for cobalt-based metal sulfides, resulting in different morphologies. Different synthesis methods significantly affect composition and morphology, making the control of microstructure necessary. Traditional template methods are complex and produce numerous byproducts, presenting certain drawbacks; metal-organic frameworks (MOFs) offer a promising alternative. MOFs (Metal-Organic Facility-Based Elements) are porous framework compounds formed through the self-assembly of metal ions and organic ligands. They possess rich topological structures. Metal sulfides derived from MOFs as precursors through high-temperature carbonization and sulfidation exhibit diverse and more tunable morphologies, without agglomeration issues. The porosity, high specific surface area, and topological morphology are preserved after high-temperature treatment. For example, the conversion of ZIF-67-derived MOFs into magnetic metal / carbon or magnetic metal sulfide / carbon composites has attracted considerable interest. Although magnetic metal sulfide / carbon composites have been explored as effective microwave absorbers, contemporary research often relies on laborious vapor deposition methods in tube furnaces to achieve ZIF-67 sulfides. This process is prone to material loss and presents challenges in precisely controlling the sulfide loading. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a method for preparing Co9S8-carbon fiber composite microwave absorbing material. This preparation method, through a solvothermal method and electrospinning process, produces a composite material that effectively combines multiple loss mechanisms, achieves good impedance matching, and realizes thin, light, wide, and strong microwave absorption performance in the 2-18 GHz frequency range. It is an ideal choice for novel lightweight and efficient microwave absorbing materials.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing a Co9S8-carbon fiber composite microwave absorbing material, wherein the Co9S8-carbon fiber composite microwave absorbing material comprises a hollow Co9S8 structure and a carbon fiber skeleton, wherein the hollow Co9S8 structure is embedded in the carbon fiber skeleton; the preparation method includes the following steps:

[0006] Step 1: Dissolve cobalt salt in deionized water to obtain a cobalt salt solution, dissolve 2-methylimidazole in deionized water to obtain a 2-methylimidazole solution, mix the cobalt salt solution and the 2-methylimidazole solution and ultrasonically disperse them to generate a precursor solution containing the coordination polymer ZIF-67.

[0007] Ethylene glycol and deionized water are mixed as a mixed solvent, and then thioacetamide is added to form a thioacetamide solution.

[0008] The above thioacetamide solution was mixed with the precursor solution, ultrasonically dispersed and magnetically stirred, and then transferred to a high-pressure reactor for solvothermal reaction. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed and dried to obtain Co3S4 / ZIF-67 composite powder.

[0009] Step 2: Dissolve polyacrylonitrile in N,N-dimethylformamide and stir at room temperature for 4-12 hours to form a uniform and transparent solution. Add the Co3S4 / ZIF-67 composite powder prepared above and stir thoroughly to obtain a Co3S4 / ZIF-67-PAN mixed solution.

[0010] Step 3: Take out the Co3S4 / ZIF-67-PAN mixed solution and prepare Co3S4 / ZIF-67-PAN composite fiber by electrospinning process;

[0011] Step 4: Place the Co3S4 / ZIF-67-PAN composite fiber in a tube furnace and calcine it at 600-900℃ for 1-5 hours in an argon atmosphere. The resulting composite material includes a carbon fiber skeleton and a hollow Co9S8 embedded in the carbon fiber skeleton, denoted as Co9S8-carbon fiber composite microwave absorbing material.

[0012] Further improvements to the preparation method of Co9S8-carbon fiber composite microwave absorbing material:

[0013] Preferably, in step 1, the concentration of the cobalt salt solution is 0.04-0.1 mol / L, and the concentration of the 2-methylimidazole solution is 1-1.5 mol / L; when the cobalt salt solution and the 2-methylimidazole solution are mixed, the molar ratio of the cobalt salt in the cobalt salt solution to the 2-methylimidazole in the 2-methylimidazole solution is 1:(10-40).

[0014] Preferably, in step 1, ethylene glycol and deionized water are mixed in a volume ratio of 2:1 as a mixed solvent, and the concentration of thioacetamide in the thioacetamide solution is 0.05-0.2 mol / L.

[0015] Preferably, in step 1, the thioacetamide solution and the precursor solution are mixed at a volume ratio of 1:(0.2-5), then ultrasonically dispersed for 10-50 min, and then magnetically stirred for 10-50 min. The temperature of the solvothermal reaction is 120-180℃, and the time is 8-24 h.

[0016] Preferably, the drying temperature in step 1 is 30-70℃ and the time is 8-24h.

[0017] Preferably, in step 2, the concentration of polyacrylonitrile in N,N-dimethylformamide is 0.05-0.2 g / mL, and the mass ratio of polyacrylonitrile to Co3S4 / ZIF-67 composite powder is (1-5):1.

[0018] Preferably, in step 3, the parameters of the electrospinning process are as follows: receiving distance is 10-30cm, spinning solution flow rate is 0.5-2mL / h, applied electrostatic voltage is 16-21kV, receiving drum speed is 100-1000rpm, temperature is 20-25℃, humidity is 4-10RH, and spinning time is 8-12h.

[0019] Preferably, in step 4, the temperature is increased to the calcination temperature at a heating rate of 1-5℃ / min.

[0020] The second objective of this invention is to provide a Co9S8-carbon fiber composite microwave absorbing material prepared by any of the above-mentioned methods.

[0021] The third objective of this invention is to provide an application of the above-mentioned Co9S8-carbon fiber composite absorbing material in the field of electromagnetic wave absorption.

[0022] The advantages of this invention compared to the prior art are as follows:

[0023] 1) This invention discloses a Co9S8-carbon fiber composite microwave absorbing material and its preparation method. The invention uses methylimidazole as an organic ligand, reacting it with a cobalt salt to obtain a coordination polymer ZIF-67. Then, a sulfur source is directly introduced into ZIF-67 via a simple solvothermal method, directly vulcanizing to obtain a hollow Co3S4 / ZIF-67 composite. The Co3S4 / ZIF-67 composite is then added to an N,N-dimethylformamide solution of polyacrylonitrile, composited via electrospinning, and further carbonized at high temperature to obtain the Co9S8-carbon fiber composite microwave absorbing material.

[0024] 2) The solvothermal method of this invention has several advantages: on the one hand, the polyhedral morphology of ZIF-67 is preserved; on the other hand, it promotes the direct formation of metal sulfides without laborious procedures and leads to the formation of hollow structures through sulfur source etching. This hollow structure promotes multiple reflections and scattering of electromagnetic waves. Incorporating this unique hollow metal sulfide structure into carbon fibers is expected to solve the impedance mismatch problem typically associated with carbon fibers. Specifically, combining hollow metal sulfides with carbon fibers results in a non-uniform structure. This structural modification not only enhances the interfacial polarization relaxation process but also improves impedance matching due to its unique dielectric and magnetic properties. Our research utilizes coordinated multi-component interactions, non-uniform interfacial polarization, multiple reflections and scattering, and the inherent magnetic loss mechanism of MOF-derived metal sulfides. These innovations work together to significantly improve the microwave absorption performance of the absorber.

[0025] 3) This invention introduces a hollow metal sulfide, Co9S8, into carbon fibers to achieve tunable microwave absorption performance, overcoming the inherent limitations of single carbon fiber materials. Co9S8 is strung together on the carbon fibers like a string of candied hawthorns through electrospinning, and tunable microwave absorption performance is achieved through controllable carbonization temperature. Satisfactory microwave absorption performance is obtained: excellent reflection loss (RL) of -60.83dB at a frequency of 10.85GHz (X-band), corresponding to a thickness of 2.76mm; furthermore, when the thickness reaches 2.19mm, the effective absorption bandwidth extends to 5.6GHz, exhibiting over 90% effective absorption of electromagnetic waves in the 12GHz–17.6GHz frequency band. The resulting composite microwave absorbing material possesses key characteristics such as lightweight, thinness, effective absorption bandwidth, and high reflection loss. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0027] Figure 1 This is a flowchart of the present invention;

[0028] Figure 2 This is a scanning electron microscope image of the Co9S8-carbon fiber composite microwave absorbing material prepared in Example 2 of the present invention;

[0029] Figure 3 The diagram shows the reflection loss of the Co9S8-carbon fiber composite microwave absorbing material prepared in Example 3 of this invention at different thicknesses. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0031] Example 1

[0032] This embodiment provides a method for preparing a Co9S8-carbon fiber composite microwave absorbing material, which specifically includes the following steps:

[0033] Step 1, Preparation of the Co3S4 / ZIF-67 complex:

[0034] 0.437 g of Co(NO3)2·6H2O was dissolved in 25 mL of deionized water and stirred until homogeneous to obtain a cobalt salt solution with a concentration of 0.06 mol / L; 2.956 g of 2-methylimidazole was dissolved in 25 mL of deionized water and stirred until homogeneous to obtain a 2-methylimidazole solution with a concentration of 1.44 mol / L; the molar ratio of cobalt salt in the cobalt salt solution to 2-methylimidazole in the 2-methylimidazole solution was 1:24; the cobalt salt solution and the 2-methylimidazole solution were mixed and sonicated for 30 min to generate a precursor solution containing the coordination polymer ZIF-67;

[0035] A mixed solution was prepared by mixing ethylene glycol (20 mL) and deionized water (10 mL) as a mixed solvent, and adding thioacetamide to a concentration of 0.13 mol / L.

[0036] The mixed solution was mixed with the above precursor solution, ultrasonicated and magnetically stirred for half an hour, and then transferred to a 100 mL Teflon-lined autoclave. It was heated to 180 °C and kept at 16 hours. After the reaction was completed, it was cooled to room temperature. The reaction solution was centrifuged at high speed, and the separated solids were washed repeatedly with deionized water and ethanol, and then dried in a vacuum oven at 55 °C for 20 hours to obtain Co3S4 / ZIF-67 composite powder.

[0037] Step 2, prepare a Co3S4 / ZIF-67-PAN mixed solution

[0038] 1.2 g of polyacrylonitrile was dissolved in 10 mL of N,N-dimethylformamide solution, with a concentration of 0.12 g / mL. The solution was stirred at room temperature for 12 h to form a uniform and transparent solution. Then, 1.2 g of Co3S4 / ZIF-67 composite powder obtained in step 1 was added. The mass ratio of polyacrylonitrile to Co3S4 / ZIF-67 composite powder was 1:1. The solution was stirred thoroughly to obtain a Co3S4 / ZIF-67-PAN mixed solution.

[0039] Step 3: Preparation of Co3S4 / ZIF-67-PAN composite fibers

[0040] The Co3S4 / ZIF-67-PAN mixed solution from step 2 was drawn into a 10mL syringe and placed into an electrospinning machine to prepare Co3S4 / ZIF-67-PAN composite fibers. The electrospinning conditions were as follows: receiving distance of 15cm, spinning solution flow rate of 1.2mL / h, applied electrostatic voltage of 18kV, receiving roller speed of 300rpm, spinning time of 10h, temperature of 22℃, and humidity of 6RH.

[0041] Step 4: Preparation of Co9S8-carbon fiber composite microwave absorbing material

[0042] Co3S4 / ZIF-67-PAN composite fibers were placed in a tube furnace and heated to 600℃ in an argon atmosphere at a heating rate of 3℃ / min. The mixture was then calcined at this temperature for 3 hours to obtain Co9S8-carbon fiber composite microwave absorbing material 1.

[0043] The prepared Co9S8-carbon fiber composite microwave absorbing material 1 was added to paraffin wax and mixed uniformly at a concentration of 50 wt%. It was then pressed into a coaxial ring with an outer diameter of 7.00 mm and an inner diameter of 3.04 mm. The reflection loss of the Co9S8-carbon fiber composite microwave absorbing material at different thicknesses was measured. Electromagnetic parameters were measured using a vector network analyzer (AV3672B-S) with the coaxial method, at frequencies ranging from 2 to 18 GHz. The results showed that the minimum reflection loss RL value of the Co9S8-CF microwave absorber was -56.37 dB, and the effective absorption bandwidth EAB was 1.7 GHz.

[0044] Example 2

[0045] This embodiment provides a method for preparing Co9S8-carbon fiber composite microwave absorbing material. The specific steps are the same as in Embodiment 1, except that in step 4, the Co3S4 / ZIF-67-PAN composite fiber is calcined in a tube furnace at a temperature of 700°C, and finally Co9S8-carbon fiber composite microwave absorbing material 2 is obtained.

[0046] Figure 2 The image shows a scanning electron microscope (SEM) image of the Co9S8-carbon fiber composite microwave absorbing material 2 prepared above; (The image is from...) Figure 2 It can be clearly seen that Co9S8 loaded on carbon fiber presents a "candied hawthorn" shape.

[0047] The prepared Co9S8-carbon fiber composite microwave absorbing material 2 was added to paraffin wax and mixed uniformly at a concentration of 50 wt%. It was then pressed into a coaxial ring with an outer diameter of 7.00 mm and an inner diameter of 3.04 mm. The reflection loss of the Co9S8-carbon fiber composite microwave absorbing material at different thicknesses was tested. Electromagnetic parameters were measured using a vector network analyzer (AV3672B-S) with the coaxial method, at frequencies ranging from 2 to 18 GHz. The results are as follows: Figure 3 As shown, the Co9S8-CF microwave absorber has a minimum reflection loss RL value of -60.83dB and an effective absorption bandwidth EAB of 5.6GHz.

[0048] Example 3

[0049] This embodiment provides a method for preparing Co9S8-carbon fiber composite microwave absorbing material. The specific steps are the same as in Embodiment 1, except that in step 4, the Co3S4 / ZIF-67-PAN composite fiber is calcined in a tube furnace at a temperature of 800°C, and finally Co9S8-carbon fiber composite microwave absorbing material 3 is obtained.

[0050] The prepared Co9S8-carbon fiber composite microwave absorbing material 3 was added to paraffin wax and mixed uniformly at a concentration of 50 wt%. It was then pressed into a coaxial ring with an outer diameter of 7.00 mm and an inner diameter of 3.04 mm. The reflection loss of the Co9S8-carbon fiber composite microwave absorbing material at different thicknesses was measured. Electromagnetic parameters were measured using a vector network analyzer (AV3672B-S) with the coaxial method, at frequencies ranging from 2 to 18 GHz. The results showed that the minimum reflection loss RL value of the Co9S8-CF microwave absorber was -9.25 dB, and the effective absorption bandwidth EAB was 0 GHz.

[0051] Example 4

[0052] This embodiment provides a method for preparing Co9S8-carbon fiber composite microwave absorbing material. The specific steps are the same as in Embodiment 2, except that: in step 2, 0.6g of Co3S4 / ZIF-67 powder obtained in step 1 is added, and the mass ratio of polyacrylonitrile to Co3S4 / ZIF-67 composite powder is 2:1, and finally Co9S8-carbon fiber composite microwave absorbing material 4 is obtained.

[0053] The prepared Co9S8-carbon fiber composite microwave absorbing material 4 was added to paraffin wax and mixed uniformly at a concentration of 50 wt%. It was then pressed into a coaxial ring with an outer diameter of 7.00 mm and an inner diameter of 3.04 mm. The reflection loss of the Co9S8-carbon fiber composite microwave absorbing material at different thicknesses was measured. Electromagnetic parameters were measured using a vector network analyzer (AV3672B-S) with the coaxial method, at frequencies ranging from 2 to 18 GHz. The results showed that the minimum reflection loss RL value of the Co9S8-CF microwave absorber was -13.91 dB, and the effective absorption bandwidth EAB was 3.5 GHz.

[0054] Example 5

[0055] This embodiment provides a method for preparing Co9S8-carbon fiber composite microwave absorbing material. The specific steps are the same as in Embodiment 2, except that: in step 2, 0.3g of Co3S4 / ZIF-67 powder obtained in step 1 is added, and the mass ratio of polyacrylonitrile to Co3S4 / ZIF-67 composite powder is 4:1, and finally Co9S8-carbon fiber composite microwave absorbing material 5 is obtained.

[0056] The prepared Co9S8-carbon fiber composite microwave absorbing material 5 was added to paraffin wax and mixed uniformly at a concentration of 50 wt%. It was then pressed into a coaxial ring with an outer diameter of 7.00 mm and an inner diameter of 3.04 mm. The reflection loss of the Co9S8-carbon fiber composite microwave absorbing material at different thicknesses was measured. Electromagnetic parameters were measured using a vector vector network analyzer (AV3672B-S) with the coaxial method, at frequencies ranging from 2 to 18 GHz. The results showed that the minimum reflection loss RL value of the Co9S8-CF microwave absorber was -21.50 dB, and the effective absorption bandwidth EAB was 5.25 GHz.

[0057] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments. It should be noted that many modifications and improvements can be made by those skilled in the art, and all modifications or improvements not exceeding the scope of the claims should be considered within the protection scope of the present invention.

Claims

1. A preparation method of a Co9S8-carbon fiber composite wave-absorbing material, characterized in that, The steps include the following: Step 1: Dissolve cobalt salt in deionized water to obtain a cobalt salt solution, dissolve 2-methylimidazole in deionized water to obtain a 2-methylimidazole solution, mix the cobalt salt solution and the 2-methylimidazole solution and ultrasonically disperse them to generate a precursor solution containing the coordination polymer ZIF-67. Ethylene glycol and deionized water are mixed as a mixed solvent, and then thioacetamide is added to form a thioacetamide solution. The above thioacetamide solution was mixed with the precursor solution, ultrasonically dispersed and magnetically stirred, and then transferred to a high-pressure reactor for solvothermal reaction. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed and dried to obtain Co3S4 / ZIF-67 composite powder. Step 2: Dissolve polyacrylonitrile in N,N-dimethylformamide and stir thoroughly to form a uniform and transparent solution. Add the Co3S4 / ZIF-67 composite powder prepared above and stir thoroughly to obtain a Co3S4 / ZIF-67-PAN mixed solution. Step 3: Take out the Co3S4 / ZIF-67-PAN mixed solution and prepare Co3S4 / ZIF-67-PAN composite fiber by electrospinning process; Step 4: Place the Co3S4 / ZIF-67-PAN composite fiber in a tube furnace and calcine it at 600-900℃ for 1-5 hours in an argon atmosphere. The resulting composite material includes a carbon fiber skeleton and a hollow Co9S8 embedded in the carbon fiber skeleton, denoted as Co9S8-carbon fiber composite microwave absorbing material.

2. The preparation method of the Co9S8-carbon fiber composite wave-absorbing material according to claim 1, characterized in that, In step 1, the concentration of the cobalt salt solution is 0.04-0.1 mol / L, and the concentration of the 2-methylimidazole solution is 1-1.5 mol / L; when the cobalt salt solution and the 2-methylimidazole solution are mixed, the molar ratio of the cobalt salt in the cobalt salt solution to the 2-methylimidazole in the 2-methylimidazole solution is 1:(10-40).

3. The preparation method of the Co9S8-carbon fiber composite wave-absorbing material according to claim 1, characterized in that, In step 1, ethylene glycol and deionized water are mixed in a volume ratio of 2:1 as a mixed solvent, and the concentration of thioacetamide in the thioacetamide solution is 0.05-0.2 mol / L.

4. The preparation method of the Co9S8-carbon fiber composite wave-absorbing material according to claim 2 or 3, characterized in that, In step 1, the thioacetamide solution and the precursor solution are mixed at a volume ratio of 1:(0.2-5), then ultrasonically dispersed for 10-50 min, and then magnetically stirred for 10-50 min. The temperature of the solvothermal reaction is 120-180℃, and the time is 8-24 h.

5. The preparation method of the Co9S8-carbon fiber composite wave-absorbing material according to claim 1, characterized in that, The drying temperature in step 1 is 30-70℃, and the time is 8-24 hours.

6. The preparation method of the Co9S8-carbon fiber composite wave-absorbing material according to claim 1, characterized in that, In step 2, the concentration of polyacrylonitrile in N,N-dimethylformamide is 0.05-0.2 g / mL, and the mixture is stirred at room temperature for 4-12 h; the mass ratio of polyacrylonitrile to Co3S4 / ZIF-67 composite powder is (1-5):

1.

7. The preparation method of the Co9S8-carbon fiber composite wave-absorbing material according to claim 1, characterized in that, In step 3, the parameters of the electrospinning process are as follows: receiving distance is 10-30cm, spinning solution flow rate is 0.5-2mL / h, applied electrostatic voltage is 16-21kV, receiving drum speed is 100-1000rpm, temperature is 20-25℃, humidity is 4-10RH, and spinning time is 8-12h.

8. The method for preparing a Co9S8-carbon fiber composite microwave absorbing material according to claim 1, characterized in that, In step 4, the temperature is increased to the calcination temperature at a heating rate of 1-5℃ / min.

9. A Co9S8-carbon fiber composite microwave absorbing material prepared by the preparation method of any one of claims 1-8.

10. The application of the Co9S8-carbon fiber composite absorbing material as described in claim 9 in the field of electromagnetic wave absorption.

Images