Graphene wave-absorbing composite material and preparation method thereof

Abstract

The application belongs to the technical field of wave-absorbing materials, and particularly discloses a graphene wave-absorbing composite material and a preparation method thereof. The material comprises graphene sheet layers and nickel and / or cobalt uniformly stacked on the graphene sheet layers in a square structure. The preparation method comprises the following steps: adding a precipitant into a dispersion system containing nickel ions and / or cobalt ions and graphene oxide, and uniformly mixing to obtain a reaction mixture; preparing a suspension through a hydrothermal method, and then performing filtration and washing on the suspension, and then performing freeze-drying and low-temperature calcination to obtain the composite material. The graphene wave-absorbing composite material prepared by the application has a reflection loss of as low as-67.1 dB, and an effective bandwidth of more than 8 GHz.

Description

Technical Field

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

[0002] With the rapid development and miniaturization of electronic technologies such as wireless communication and mobile devices, excessive electromagnetic radiation has been recognized as the fourth leading cause of pollution, seriously threatening human health. The attenuation capability of microwave absorbing materials, which can actively absorb microwave radiation and convert its energy into heat or dispersed microwave interference, is of great significance. Extensive research has been devoted to creating highly efficient microwave absorbing materials to reduce electromagnetic pollution.

[0003] Graphene possesses advantages such as high carrier mobility, low density, and large specific surface area, exhibiting enormous potential for microwave absorption. However, using graphene alone as an absorber results in generally poor microwave absorption performance due to its high conductivity, simple loss mechanism, and reduced interfacial impedance matching. Assembling graphene with magnetic nanoparticles to adjust and balance the electromagnetic parameters of the absorbing material is a feasible method to improve microwave absorption performance. Assembling or doping different magnetic nanoparticles on materials such as nanosheets, fibers, or core / shell nanostructures, such as CoNi and Ag-modified graphene, hollow nickel nanocore-modified reduced graphene oxide, and Fe3O4-modified reduced graphene oxide, has successfully prepared many composite materials to improve the impedance matching of pure graphene. Furthermore, charge transfer at the graphene interface, polarization relaxation of free carriers in graphene, electromagnetic connections between graphene and magnetic particles, and the significant scattering and reflection generated by the superimposed wrinkles in the composite material also improve the microwave absorption performance of the composite material. However, the narrow bandwidth and complex manufacturing process of magnetic particle-modified graphene microwave absorbing composite materials still limit their production and application.

[0004] Patent CN110157266A discloses a high thermal conductivity graphene microwave absorbing composite material and its preparation method. The graphene microwave absorbing material is prepared by combining a graphene film with a microwave absorbing material. The microwave absorbing material serves as the substrate, and the raw materials for the graphene film include graphene, an organic polymer solution, and a resin. This patent aims to improve the thermal conductivity of microwave absorbing materials using a graphene film. Summary of the Invention

[0005] To address the shortcomings of the existing technologies, this invention provides a graphene microwave absorbing composite material with ultra-wideband microwave absorption, in which nickel and / or cobalt particles are supported in a tetragonal stacked structure, and a method for preparing the same.

[0006] This invention is achieved through the following technical solutions.

[0007] A graphene-based microwave absorbing composite material includes: graphene sheets and nickel and / or cobalt; the nickel and / or cobalt are uniformly stacked on the graphene sheets in a tetragonal structure.

[0008] A method for preparing the above-mentioned graphene microwave absorbing composite material includes:

[0009] (1) A precipitant is added to a dispersion system containing nickel ions and / or cobalt ions and graphene oxide and mixed evenly to obtain a reaction mixture, wherein the precipitant is oxalate ions;

[0010] (2) The reaction mixture obtained in step (1) is prepared into a suspension by hydrothermal method. The suspension is then filtered, washed, freeze-dried, and finally calcined at low temperature to obtain the graphene microwave absorbing composite material.

[0011] Preferably, in step (1), the raw material for nickel ions is at least one of nickel nitrate, nickel sulfate, nickel chloride and nickel acetate; the raw material for cobalt ions is at least one of cobalt nitrate, cobalt sulfate, cobalt chloride and cobalt acetate; and the raw material for oxalate ions is at least one of oxalic acid, ammonium oxalate and sodium oxalate.

[0012] Preferably, the mass ratio of graphene oxide to nickel and / or cobalt is 10 to 1:1; and the molar ratio of oxalate ions to nickel and / or cobalt is 25 to 1:1.

[0013] Preferably, the mass ratio of graphene oxide to nickel and / or cobalt is 6 to 1:1; and the molar ratio of oxalate ions to nickel and / or cobalt is 10 to 1:1.

[0014] Preferably, in step (1), an additive is added to the reaction mixture. The additive is one or more of polyethylene glycol, polyvinyl alcohol, polyethyleneimine, polydimethylammonium chloride, and methylcellulose. The amount of the additive added is 0 to 2% (by mass) of graphene oxide.

[0015] Preferably, the amount of the additive is 0 to 1% of the graphene oxide.

[0016] Preferably, in step (1), the pH of the reaction system is controlled to be 2-9; in step (2), the hydrothermal conditions are 110-200℃ for 1-48h.

[0017] Preferably, in step (1), the pH of the reaction system is controlled to be 6-9; in step (2), the hydrothermal conditions are 120-180℃ for 4-24h.

[0018] Preferably, in step (2), the freeze-drying conditions are drying in an environment with a temperature below -45°C and a vacuum degree below 0.1Pa for 24 to 96 hours.

[0019] Preferably, in step (2), the product is calcined at a low temperature of 200–600°C for 1–12 hours under a vacuum, nitrogen, or argon protective atmosphere.

[0020] Preferably, in step (2), the product is calcined at 300-500°C for 1-12 hours.

[0021] The graphene absorbing composite material prepared by this invention can have a reflection loss as low as -67.1dB and an effective bandwidth of over 8GHz.

[0022] Beneficial technical effects of the present invention:

[0023] 1) In the graphene microwave absorbing composite material provided by the present invention, nickel and / or cobalt particles are stacked on the graphene sheets in a tetragonal structure.

[0024] 2) The tetragonal stacked nickel / cobalt particles expand the layered graphene, increasing interfacial and magnetic losses and improving the impedance matching characteristics of the resulting composite material. In addition, the large amount of scattering and reflection generated by the superimposed wrinkles in the composite material also improves the absorption performance of the composite material, giving it excellent ultra-wideband absorption performance.

[0025] 3) The preparation process of the graphene microwave absorbing composite material provided by the present invention is simple, and the required process equipment and raw materials are inexpensive and readily available, and have the potential for industrial production and application. Attached Figure Description

[0026] Figure 1 SEM images of nickel oxalate, nickel oxalate / cobalt, and cobalt oxalate;

[0027] Figure 2 SEM images of nickel / graphene, nickel / cobalt / graphene, and cobalt / graphene composites;

[0028] Figure 3 XRD of nickel / cobalt / graphene composite material;

[0029] Figure 4 The 3D reflectivity and absorption bandwidth (EAB) of nickel / graphene composites at different thermal reduction temperatures are shown. Detailed Implementation

[0030] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0031] Example 1

[0032] 1) Dissolve 400 mg of graphene oxide in 50 ml of deionized water and disperse using ultrasound for 60 minutes to form a brown graphene oxide solution. Dissolve 1982 mg of Ni(NO3)2·6H2O in 10 ml of deionized water to obtain a nickel nitrate solution. Combine the brown graphene oxide suspension with the nickel nitrate solution and stir for 30 minutes. Dissolve 1719 mg of H2C2O4·2H2O in 10 ml of deionized water to obtain an oxalic acid solution. Slowly add the oxalic acid solution to the mixture of nickel nitrate solution and graphene suspension, and stir for 30 minutes to obtain the reaction mixture. Control the pH of the reaction system to 5-7.

[0033] 2) The reaction mixture was placed in a 100ml Teflon-lined stainless steel autoclave and reacted at 150℃ for 7h to obtain a suspension. The suspension was filtered and washed, and centrifuged three times with deionized water for 3 minutes each time. Then it was freeze-dried at -45℃ and below vacuum of 0.1Pa for 24h and calcined at 400℃ for 2h to obtain a graphene composite microwave absorbing material with nickel particles stacked in a tetragonal structure.

[0034] In this embodiment, the nickel / graphene composite microwave absorbing material was mixed with 85% paraffin to form a ring-shaped sample with an outer diameter of 7 mm and an inner diameter of 3.04 mm. The electromagnetic parameters of the sample in the 2-18 GHz range were measured using the coaxial method and a vector network analyzer, and the reflection loss of the composite material was calculated using CST software. The lowest reflection loss was -67.1 dB, and the effective bandwidth EAB was 8.66 GHz.

[0035] Example 2

[0036] 1) Dissolve 400 mg of graphene oxide in 50 ml of deionized water and disperse using ultrasound for 60 minutes to form a brown graphene oxide solution. Dissolve 495 mg of Ni(NO3)2·6H2O and 495 mg of Co(NO3)2·6H2O in 10 ml of deionized water to obtain a nickel nitrate / cobalt solution. Combine the brown graphene oxide suspension with the nickel nitrate / cobalt solution and stir for 30 minutes. Dissolve 10296 mg of H2C2O4·2H2O in 10 ml of deionized water to obtain an oxalic acid solution. Slowly add the oxalic acid solution to the mixture of nickel nitrate / cobalt solution and graphene suspension, and stir for 30 minutes to obtain the reaction mixture. Control the pH of the reaction system to 4-6.

[0037] 2) The reaction mixture was placed in a 100ml Teflon-lined stainless steel autoclave and reacted at 200℃ for 1h to obtain a suspension. The suspension was filtered and washed, and centrifuged three times with deionized water for 3 minutes each time. Then it was freeze-dried for 24h and calcined at 500℃ for 1h to obtain a graphene composite material with nickel / cobalt particles stacked in a tetragonal structure.

[0038] In this embodiment, a tetragonal stacked nickel / cobalt / graphene composite material was prepared and mixed with 85% paraffin to form a ring-shaped mixture sample with an outer diameter of 7 mm and an inner diameter of 3.04 mm. The electromagnetic parameters of the sample in the 2-18 GHz range were measured using the coaxial method and a vector network analyzer. The reflection loss of the composite material was then calculated using CST software. The lowest reflection loss was -27.1 dB, and the effective bandwidth EAB was 8.75 GHz.

[0039] Example 3

[0040] 1) Dissolve 400 mg of graphene oxide in 50 ml of deionized water and disperse using ultrasound for 60 minutes to form a brown graphene oxide solution. Dissolve 658 mg of Co(NO3)2·6H2O in 10 ml of deionized water to obtain a cobalt nitrate solution. Combine the brown graphene oxide suspension with the cobalt nitrate solution and stir for 30 minutes. Dissolve 1120 mg of H2C2O4·2H2O in 10 ml of deionized water to obtain an oxalic acid solution. Slowly add the oxalic acid solution to the mixture of cobalt nitrate solution and graphene suspension, and stir for 30 minutes to obtain the reaction mixture. Control the pH of the reaction system to 5-7.

[0041] 2) The reaction mixture was placed in a 100ml Teflon-lined stainless steel autoclave and reacted at 120℃ for 12h to obtain a suspension. The suspension was filtered and washed, and centrifuged three times with deionized water for 3 minutes each time. Then it was freeze-dried for 24h and calcined at 400℃ for 1h to obtain a cobalt particle tetragonal stacked graphene composite material.

[0042] In this embodiment, the cobalt / graphene composite material was mixed with 85% paraffin to form a ring-shaped sample with an outer diameter of 7 mm and an inner diameter of 3.04 mm. The electromagnetic parameters of the sample in the 2-18 GHz range were measured using the coaxial method and a vector network analyzer, and the reflection loss of the composite material was calculated using CST software. The lowest reflection loss was -45.3 dB, and the effective bandwidth EAB was 8.32 GHz.

[0043] Example 4

[0044] 400 mg of graphene oxide and 0.4 mg of polyethylene glycol were dissolved in 50 ml of deionized water and dispersed ultrasonically for 60 minutes to form a brown graphene oxide solution. 212 mg of Ni(NO3)2·6H2O was dissolved in 10 ml of deionized water to obtain a nickel nitrate solution. The brown graphene oxide suspension was combined with the nickel nitrate solution and stirred for 30 minutes. 1719 mg of H2C2O4·2H2O was dissolved in 10 ml of deionized water to obtain an oxalic acid solution. The oxalic acid solution was slowly added to the mixture of nickel nitrate solution and graphene suspension, and stirred for 30 minutes to obtain the reaction mixture. The pH of the reaction system was controlled at 5-7.

[0045] 2) The reaction mixture was placed in a 100ml Teflon-lined stainless steel autoclave and reacted at 180℃ for 4h to obtain an olefin suspension. The suspension was filtered and washed, and centrifuged three times with deionized water for 3 minutes each time. Then it was freeze-dried for 24h and calcined at 200℃ for 12h to obtain a nickel particle tetragonal stacked graphene composite material.

[0046] In this embodiment, the nickel / graphene composite material was mixed with 85% paraffin to form a ring-shaped mixture sample with an outer diameter of 7 mm and an inner diameter of 3.04 mm. The coaxial method was used for testing, and the electromagnetic parameters of the sample in the 2-18 GHz range were measured using a vector network analyzer. The reflection loss of the composite material was then calculated using CST software. The lowest reflection loss was -22.3 B, and the effective bandwidth EAB was 8.51 GHz.

[0047] Example 5

[0048] 400 mg of graphene oxide and 0.2 mg of polyvinyl alcohol were dissolved in 50 ml of deionized water and dispersed ultrasonically for 60 minutes to form a brown graphene oxide solution. 272 ​​mg of Ni(NO3)2·6H2O and 232 mg of (CH3COO)2Co·4H2O were dissolved in 10 ml of deionized water to obtain a nickel / cobalt ion solution. The brown graphene oxide suspension was combined with the nickel / cobalt ion solution and stirred for 30 minutes. 2240 mg of H2C2O4·2H2O was dissolved in 10 ml of deionized water to obtain an oxalic acid solution. The oxalic acid solution was slowly added to the mixture of the nickel / cobalt ion solution and the graphene suspension, and stirred for 30 minutes to obtain the reaction mixture. The pH of the reaction system was controlled at 5-7.

[0049] 2) The reaction mixture was placed in a 100ml Teflon-lined stainless steel autoclave and reacted at 110℃ for 48h to obtain a suspension. The suspension was filtered and washed, and centrifuged three times with deionized water for 3 minutes each time. Then it was freeze-dried for 24h and calcined at 500℃ for 1h to obtain a graphene composite material with nickel / cobalt particles stacked in a tetragonal structure.

[0050] In this embodiment, the nickel / cobalt / graphene composite material was mixed with 85% paraffin to form a ring-shaped sample with an outer diameter of 7 mm and an inner diameter of 3.04 mm. The electromagnetic parameters of the sample in the 2-18 GHz range were measured using the coaxial method and a vector network analyzer, and the reflection loss of the composite material was calculated using CST software. The lowest reflection loss was -19.1 dB, and the effective bandwidth EAB was 8.92 GHz.

[0051] Example 6

[0052] 400 mg of graphene oxide and 0.3 mg of polydienedimethylammonium chloride were dissolved in 50 ml of deionized water and dispersed ultrasonically for 60 minutes to form a brown graphene oxide solution. 396 mg of Ni(CH3COO)2·4H2O and 846 mg of (CH3COO)2Co·4H2O were dissolved in 10 ml of deionized water to obtain a nickel acetate / cobalt solution. The brown graphene oxide suspension was combined with the nickel acetate / cobalt solution and stirred for 30 minutes. 1693 mg of (NH4)2C2O4 was dissolved in 10 ml of deionized water to obtain an ammonium oxalate solution. The ammonium oxalate solution was slowly added to the mixture of the nickel acetate / cobalt solution and the graphene suspension, and stirred for 30 minutes to obtain the reaction mixture, maintaining the pH of the reaction system at 7-9.

[0053] 2) The reaction mixture was placed in a 100ml Teflon-lined stainless steel autoclave and reacted at 160℃ for 6h to obtain a suspension. The suspension was filtered and washed, and centrifuged three times with deionized water for 3 minutes each time. Then it was freeze-dried for 50h and calcined at 350℃ for 6h to obtain a graphene composite material with nickel / cobalt particles stacked in a tetragonal structure.

[0054] In this embodiment, the nickel / cobalt / graphene composite material was mixed with 85% paraffin to form a ring-shaped sample with an outer diameter of 7 mm and an inner diameter of 3.04 mm. The electromagnetic parameters of the sample in the 2-18 GHz range were measured using the coaxial method and a vector network analyzer, and the reflection loss of the composite material was calculated using CST software. The lowest reflection loss was -22.3 dB, and the effective bandwidth EAB was 8.11 GHz.

[0055] Example 7

[0056] 400 mg of graphene oxide and 0.8 mg of polydienedimethylammonium chloride were dissolved in 50 ml of deionized water and dispersed ultrasonically for 60 minutes to form a brown graphene oxide solution. 290 mg of Ni(CH3COO)2·4H2O and 495 mg of Co(NO3)2·6H2O were dissolved in 10 ml of deionized water to obtain a nickel / cobalt ion solution. The brown graphene oxide suspension was combined with the nickel / cobalt ion solution and stirred for 30 minutes. 560 mg of (NH4)2C2O4 was dissolved in 10 ml of deionized water to obtain an ammonium oxalate solution. The ammonium oxalate solution was slowly added to the mixture of the nickel / cobalt ion solution and the graphene suspension, and stirred for 30 minutes to obtain the reaction mixture. The pH of the reaction system was controlled at 7-9.

[0057] 2) The reaction mixture was placed in a 100ml Teflon-lined stainless steel autoclave and reacted at 150℃ for 5h to obtain a suspension. The suspension was filtered and washed, and centrifuged three times with deionized water for 3 minutes each time. Then it was freeze-dried for 24h and calcined at 400℃ for 10h to obtain a graphene composite material with nickel / cobalt particles stacked in a tetragonal structure.

[0058] In this embodiment, the nickel / cobalt / graphene composite material was mixed with 85% paraffin to form a ring-shaped sample with an outer diameter of 7 mm and an inner diameter of 3.04 mm. The electromagnetic parameters of the sample in the 2-18 GHz range were measured using the coaxial method and a vector network analyzer, and the reflection loss of the composite material was calculated using CST software. The lowest reflection loss was -33.2 dB, and the effective bandwidth EAB was 8.00 GHz.

[0059] Example 8

[0060] 400 mg of graphene oxide and 2 mg of polyethylene glycol were dissolved in 50 ml of deionized water and dispersed ultrasonically for 60 minutes to form a brown graphene oxide solution. 290 mg of nickel sulfate heptahydrate was dissolved in 10 ml of deionized water to obtain a nickel sulfate solution. The brown graphene oxide suspension was combined with the nickel sulfate solution and stirred for 30 minutes. 320 mg of sodium oxalate was dissolved in 10 ml of deionized water to obtain a sodium oxalate solution. The sodium oxalate solution was slowly added to the mixture of nickel sulfate solution and graphene suspension, and stirred for 30 minutes to obtain the reaction mixture. The pH of the reaction system was controlled at 6-8.

[0061] 2) The reaction mixture was placed in a 100ml Teflon-lined stainless steel autoclave and reacted at 170℃ for 28h to obtain a suspension. The suspension was filtered and washed, and centrifuged three times with deionized water for 3 minutes each time. Then it was freeze-dried for 24h and calcined at 250℃ for 6h to obtain a graphene composite material with nickel particles stacked in a tetragonal structure.

[0062] In this embodiment, the nickel / graphene composite material was mixed with 85% paraffin to form a ring-shaped sample with an outer diameter of 7 mm and an inner diameter of 3.04 mm. The electromagnetic parameters of the sample in the 2-18 GHz range were measured using the coaxial method and a vector network analyzer, and the reflection loss of the composite material was calculated using CST software. The lowest reflection loss was -40.6 dB, and the effective bandwidth EAB was 8.43 GHz.

[0063] Example 9

[0064] 400 mg of graphene oxide and 3.6 mg of methylcellulose were dissolved in 50 ml of deionized water and dispersed ultrasonically for 60 minutes to form a brown graphene oxide solution. 495 mg of cobalt sulfate heptahydrate was dissolved in 10 ml of deionized water to obtain a cobalt sulfate solution. The brown graphene oxide suspension was combined with the cobalt sulfate solution and stirred for 30 minutes. 560 mg of sodium oxalate was dissolved in 10 ml of deionized water to obtain a sodium oxalate solution. The sodium oxalate solution was slowly added to the mixture of cobalt sulfate solution and graphene suspension, and stirred for 30 minutes to obtain the reaction mixture. The pH of the reaction system was controlled at 6-8.

[0065] 2) The reaction mixture was placed in a 100ml Teflon-lined stainless steel autoclave and reacted at 170℃ for 15h to obtain a suspension. The suspension was filtered and washed, and centrifuged three times with deionized water for 3 minutes each time. Then it was freeze-dried for 80h and calcined at 220℃ for 4h to obtain a graphene composite material with cobalt particles stacked in a tetragonal structure.

[0066] In this embodiment, the cobalt / graphene composite material was mixed with 85% paraffin to form a ring-shaped sample with an outer diameter of 7 mm and an inner diameter of 3.04 mm. The coaxial method was used for testing, and the electromagnetic parameters of the sample in the 2-18 GHz range were measured using a vector network analyzer. The reflection loss of the composite material was then calculated using CST software. The lowest reflection loss was -22.4 dB, and the effective bandwidth EAB was 8.12 GHz.

[0067] Table 1 Summary of material proportions for each embodiment

[0068]

[0069] The above description is merely a preferred embodiment of the present invention and is not limited to the invention. It should be noted that those skilled in the art can make other equivalent improvements based on the technical teachings provided by the present invention, all of which can achieve the purpose of the present invention and should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a graphene microwave absorbing composite material, characterized in that, The method includes: (1) A precipitant is added to a dispersion system containing nickel ions and / or cobalt ions and graphene oxide and mixed evenly to obtain a reaction mixture. The pH of the reaction system is 2-9. The precipitant is oxalate ions. The mass ratio of graphene oxide to nickel and / or cobalt is 10-1:

1. The molar ratio of oxalate ions to nickel and / or cobalt is 25-1:

1. (2) The reaction mixture obtained in step (1) is prepared into a suspension by hydrothermal method. The hydrothermal conditions are 110-200℃ for 1-48h. The suspension is then filtered, washed, and freeze-dried. The freeze-drying conditions are drying in an environment with a temperature below -45℃ and a vacuum degree below 0.1Pa for 24-96h. Finally, the suspension is calcined at a low temperature of 200-600℃ for 1-12h under a vacuum, nitrogen or argon protective atmosphere to obtain a graphene microwave absorbing composite material. The graphene absorbing composite material comprises: graphene sheets, and nickel and / or cobalt; the nickel and / or cobalt are uniformly stacked on the graphene sheets in a tetragonal structure.

2. The preparation method according to claim 1, characterized in that, In step (1), the raw material for nickel ions is at least one of nickel nitrate, nickel sulfate, nickel chloride and nickel acetate; the raw material for cobalt ions is at least one of cobalt nitrate, cobalt sulfate, cobalt chloride and cobalt acetate; and the raw material for oxalate ions is at least one of oxalic acid, ammonium oxalate and sodium oxalate.

3. The preparation method according to claim 1, characterized in that, The mass ratio of graphene oxide to nickel and / or cobalt is 6 to 1:1; the molar ratio of oxalate ions to nickel and / or cobalt is 10 to 1:

1.

4. The preparation method according to claim 1, characterized in that, In step (1), an additive is added to the reaction mixture. The additive is one or more of polyethylene glycol, polyvinyl alcohol, polyethyleneimine, polydimethylammonium chloride, and methylcellulose. The amount of the additive added is 0 to 2% of the graphene oxide.

5. The preparation method according to claim 4, characterized in that, The amount of the additive added is 0 to 1% of the graphene oxide.

6. The preparation method according to claim 1, characterized in that, In step (1), the pH of the reaction system is controlled at 6 to 9; in step (2), the hydrothermal conditions are 120 to 180℃ for 4 to 24 hours.

7. The preparation method according to claim 1, characterized in that, In step (2), the product is calcined at a low temperature of 200–600°C for 1–12 hours under a vacuum, nitrogen or argon protective atmosphere.

8. The preparation method according to claim 1, characterized in that, In step (2), the product is calcined at 300-500℃ for 1-12 hours.

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