Preparation method and application of nickel hydroxide modified graphene composite broadband wave absorbing material

Abstract

The present invention relates to a nickel hydroxide modified graphene composite broadband wave absorbing material and a preparation method and application, belonging to the technical field of electromagnetic wave absorbing materials. The specific synthesis method is: pre-oxidation treatment is performed on the graphene raw material using hydrogen peroxide. This step creates a large number of defects on the graphene surface to create conditions for the loading of nanoparticles. Then, nickel hydroxide is loaded on the pre-treated graphene surface under the condition of different alkaline solution addition amounts. The nickel hydroxide particles under different synthesis conditions have different sizes. By adjusting the loading conditions, the modification effect of nickel hydroxide on graphene can be optimized, and the overall absorption capacity of electromagnetic waves is enhanced, thereby obtaining a broadband electromagnetic absorption material. At the same time, the synthesis process of the material is simple, the filling ratio and application thickness are low, and it can meet the needs of industrial production and has application value.

Description

Technical Field

[0001] The present invention specifically relates to a preparation method and application of a nickel hydroxide modified graphene composite broadband absorbing material, belonging to the technical field of electromagnetic wave absorbing materials. After modification by nickel hydroxide, the impedance matching of graphene is optimized, and the bandwidth of the overall material is widened. The graphene can be used as a functional filler for anti-electromagnetic interference equipment or external coating of weapons and equipment, thereby achieving electromagnetic protection or radar stealth effects. Background Art

[0002] Graphene is a two-dimensional carbon material that has been vigorously studied at home and abroad in recent years. It has a large specific surface area, excellent chemical stability and good electrical conductivity. When applied to electromagnetic wave absorption materials, due to the dielectric loss capacity of graphene itself, graphene-based absorbing materials will have certain electromagnetic absorption properties. In 2020, Nankai University published a patent CN112165849A, which mentioned that the graphene-based electromagnetic absorption material not only has a wide absorption band, but also can achieve electromagnetic absorption performance regulation by changing the voltage to adjust the material's response intensity to electromagnetic signals.

[0003] However, the conductive network structure on the surface of graphene will seriously affect the impedance matching ability of the material when it is applied in the field of wave absorption. When electromagnetic waves are incident on the surface of the material, the induced electromagnetic field will produce serious skin currents on the surface of graphene, affecting the further incidence of electromagnetic waves. Therefore, researchers design composite materials to regulate the impedance matching characteristics of graphene, thereby optimizing the wave absorption performance of graphene. In 2021, the Institute of Chemical Engineering of Guangdong Academy of Sciences published a patent CN112788935A. By regulating the electromagnetic parameters of reduced graphene oxide with nano-inorganic oxides and nano-metals, the prepared composite material has excellent electromagnetic absorption performance at high frequencies. In 2019, the 725th Institute of China Shipbuilding Industry Corporation published a patent CN109107528A, proposing the performance regulation effect of magnetic nickel metal synthesized with nickel acetate as the nickel source on graphene. After composite component design, the prepared graphene composite material can have the characteristics of low density, high coercive force, high saturation magnetization and large magnetic area. Summary of the invention

[0004] In view of the above problems, the present invention utilizes the difference in dielectric properties between nickel hydroxide and graphene, compounds the two materials by chemical means, and regulates the electromagnetic parameters of the composite material through the modification of graphene by nickel hydroxide nanoparticles, so that the impedance matching and attenuation capabilities of the material are balanced, and designs a graphene-based composite material. This material effectively broadens the electromagnetic absorption band of graphene by integrating multiple loss mechanisms, and no toxic organic solvents are used in the experimental process. It can be used as a functional stealth coating filler and coated on the surface of weapons and equipment or electromagnetic protection equipment to reduce the impact of external electromagnetic waves on the equipment body. It has a broad application market and broad economic prospects.

[0005] The first purpose of the present invention is to provide a method for preparing a nickel hydroxide modified graphene composite broadband electromagnetic wave absorbing material; the second purpose is to provide a method for regulating the electromagnetic parameters of the graphene composite broadband electromagnetic wave absorbing material by controlling the amount of alkaline ammonia added in the reaction; the third purpose is to provide the application of the graphene composite broadband electromagnetic wave absorbing material in broadening the graphene electromagnetic absorption band and improving the electromagnetic absorption performance.

[0006] In order to achieve the above object, the specific scheme adopted by the present invention is as follows:

[0007] A method for preparing a nickel hydroxide modified graphene composite broadband electromagnetic wave absorbing material, wherein the graphene composite broadband electromagnetic wave absorbing material uses graphene as a raw material, firstly oxidizes and etches the graphene, creates defects on the graphene surface to generate nickel hydroxide loading sites, and then composites the nickel hydroxide with the oxidized and etched graphene, so that nickel hydroxide nanoparticles are evenly distributed on the graphene surface, forming a nickel hydroxide modified graphene composite broadband electromagnetic wave absorbing material. The preparation method specifically comprises the following steps:

[0008] Step 1, graphene pretreatment: using a 30% by mass hydrogen peroxide solution as an etchant, adding 200-300 ml of hydrogen peroxide solution to each gram of graphene raw material, and then using distilled water to prepare a total of 500 ml of a mixed solution, after being fully dispersed, heating to 60-90 degrees Celsius and maintaining the temperature for 1-2 hours, separating the graphene and the solution, and fully washing and drying to obtain a graphene precursor;

[0009] Step 2: Take the graphene precursor obtained in step 1, add nickel nitrate hexahydrate, the mass ratio of nickel nitrate hexahydrate to graphene precursor is maintained at 8-13:1, add distilled water to disperse evenly, and obtain a dispersion;

[0010] Step 3: Mix ammonia water and distilled water evenly, then add them to the dispersion obtained in step 2, mix evenly to obtain a reaction solution, wherein the amount of ammonia water is maintained at 4%-20% of the total volume of the reaction solution; heat the reaction solution to 90-120 degrees Celsius and maintain insulation and stirring for 4 hours, separate and wash the solid phase product after the reaction is completed, and obtain a nickel hydroxide modified graphene composite broadband electromagnetic wave absorbing material.

[0011] In step 2, distilled water is added to disperse evenly. The amount of distilled water added is adjusted according to the amount of the material to be dispersed, and the standard is that all reactants can be dispersed in the solvent.

[0012] The present invention also provides a method for regulating electromagnetic parameters of a graphene composite broadband electromagnetic wave absorbing material, wherein the graphene composite broadband electromagnetic wave absorbing material is obtained by loading nickel hydroxide on the surface of graphene pretreated with hydrogen peroxide, and the synthesis method comprises the following steps:

[0013] Step 1, graphene pretreatment: using a 30% by mass hydrogen peroxide solution as an etchant, adding 200-300 ml of hydrogen peroxide solution to each gram of graphene raw material, and then using distilled water to prepare a total of 500 ml of a mixed solution, after being fully dispersed, heating to 60-90 degrees Celsius and maintaining the temperature for 1-2 hours, separating the graphene and the solution, and fully washing and drying to obtain a graphene precursor;

[0014] Step 2: Take the graphene precursor obtained in step 1, add nickel nitrate hexahydrate, the mass ratio of nickel nitrate hexahydrate to graphene precursor is maintained at 8-13:1, add distilled water to disperse evenly, and obtain a dispersion;

[0015] Step 3, mixing ammonia water and distilled water evenly, then adding them to the dispersion obtained in step 2, and mixing evenly to obtain a reaction solution, wherein the amount of ammonia water is maintained at 4%-20% of the total volume of the reaction solution; heating the reaction solution to 90-120 degrees Celsius and maintaining the temperature and stirring for 4 hours, separating and washing the solid phase product after the reaction is completed, and obtaining a nickel hydroxide modified graphene composite broadband electromagnetic wave absorbing material;

[0016] The regulation refers to adjusting the amount of ammonia water in the reaction solution in step three to achieve the particle size of the nickel hydroxide particles loaded on the graphene surface.

[0017] The present invention further provides the above-mentioned preparation method and the application of the graphene composite broadband absorbing material prepared by the preparation method in broadening the graphene electromagnetic absorption band and improving the electromagnetic absorption performance.

[0018] The present invention selects nano-scale nickel hydroxide as modified particles, improves the uniformity of the distribution of nanoparticles on the graphene surface by pre-oxidation and etching of graphene, controls the growth of nickel hydroxide on the graphene surface by designing the reaction environment of nickel hydroxide, optimizes the regulation of nickel hydroxide on graphene to the maximum extent, increases the effective absorption bandwidth of graphene-based composite materials, and broadens the application potential of graphene materials. Therefore, the composite material designed by modifying graphene with nickel hydroxide in the present invention is a wave absorbing material with simple process and excellent electromagnetic wave absorption performance, and has great research value and application market.

[0019] Beneficial effects:

[0020] The nickel hydroxide modified graphene composite broadband wave absorbing material of the present invention, the graphene raw material is subjected to oxidation pretreatment and modified by nickel hydroxide of different particle morphologies, when the corresponding matching thickness is less than 2mm, its effective absorption bandwidth can reach 6.0GHz, has a wide effective absorption bandwidth and thin filling thickness, can meet the requirements of electromagnetic wave absorbing materials for bandwidth and thickness, nickel hydroxide regulates the performance of graphene by enhancing polarization and optimizing matching, and the final synthesized composite material has excellent electromagnetic absorption performance. At the same time, the present invention does not need to use highly toxic organic solvents, the synthesis temperature can be controlled in a relatively low temperature range (below 150 degrees Celsius), the preparation process is simple, large-scale production can be achieved, and it can be used as a functional filler for electromagnetic absorption coating.

[0021] In the nickel hydroxide / graphene composite material obtained by the present invention, nickel hydroxide nanoparticles are evenly distributed on the graphene surface. By controlling the amount of alkaline ammonia added in the reaction, the particle size of the nickel hydroxide particles loaded on the graphene surface can be controlled, thereby regulating the electromagnetic parameters of the graphene composite material, optimizing the matching and loss characteristics, and thereby widening the effective absorption bandwidth of the composite material. Through the ammonia concentration embodiment regulation, under the condition of a low filling ratio of 10wt%, the effective absorption bandwidth of the synthesized nickel hydroxide / graphene composite material can cover 12-18GHz, and the matching thickness can be as low as less than 2mm, showing excellent electromagnetic wave absorption capacity. The present invention utilizes hydrogen peroxide to pre-oxidize the graphene raw material, and this step creates a large number of defects on the graphene surface to create conditions for the loading of nanoparticles. Then, nickel hydroxide is loaded on the surface of the pretreated graphene under the conditions of different amounts of alkaline solution added. The nickel hydroxide particles under different synthesis conditions have different sizes. By adjusting the loading conditions, the modification effect of nickel hydroxide on graphene can be optimized to enhance the overall absorption capacity of electromagnetic waves, thereby obtaining a broadband electromagnetic absorption material. At the same time, the synthesis process of the material is simple, the filling ratio and application thickness are low, which can meet the needs of industrial production and has application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the morphology of nickel hydroxide / graphene-1;

[0023] Figure 2 is the morphology of nickel hydroxide / graphene-2;

[0024] Figure 3 It is the XRD spectrum of graphene and nickel hydroxide modified graphene samples;

[0025] Figure 4 It is the real part spectrum of the dielectric of graphene and nickel hydroxide modified graphene samples;

[0026] Figure 5 It is the dielectric imaginary spectrum of graphene and nickel hydroxide modified graphene samples;

[0027] Figure 6 This is the Kerr curve spectrum of nickel hydroxide modified graphene sample;

[0028] Figure 7 It is a graphene raw material performance spectrum;

[0029] Figure 8 It is the performance spectrum of hydrogen peroxide treated graphene;

[0030] Fig. 9 It is the performance spectrum of nickel hydroxide / graphene-1;

[0031] Fig.10 It is the performance spectrum of nickel hydroxide / graphene-2. DETAILED DESCRIPTION

[0032] The present invention is achieved through the following technical solutions:

[0033] (1) Specifically, the present invention relates to a nickel hydroxide modified graphene composite broadband wave absorbing material and a preparation method thereof. Before the graphene and nickel hydroxide are composited, the present invention adds a step of hydrogen peroxide oxidation etching treatment. Under the action of hydrogen peroxide, the original conductive network structure of the graphene will be damaged to a certain extent, but it will not be damaged to the extent of complete fragmentation. This step can connect oxidized groups to the graphene surface on the basis of basically maintaining the original structure of the graphene, create defects to generate nickel hydroxide loading sites, and make the growth of nickel hydroxide more uniform, so as to maximize its modification effect on graphene.

[0034] (2) The nickel hydroxide modified graphene composite broadband electromagnetic wave absorbing material will grow into different morphologies under different alkaline conditions, such as low ammonia concentration and high ammonia concentration. Figure 1 and Figure 2As shown, under the condition of low ammonia addition, nickel hydroxide will grow into small particles close to hexagons and be evenly loaded on the graphene surface. Under the condition of high ammonia addition, due to the difference in reaction conditions, the nickel hydroxide particles will become very small compared with the previous ones, and a layer of nickel hydroxide nanoparticles can be evenly distributed on the graphene surface.

[0035] (3) The nickel hydroxide modified graphene composite broadband electromagnetic wave absorbing material is combined with Figure 3-X RD spectrum analysis shows that only the graphene that has been oxidized has the characteristic peak of carbon (002) at around 20°, while the nickel hydroxide-graphene composite material modified with nickel hydroxide has three characteristic peaks corresponding to nickel hydroxide: (111), (200), and (220).

[0036] (4) The electromagnetic parameters of the nickel hydroxide modified graphene composite broadband electromagnetic wave absorbing material undergo significant changes after being modified by nickel hydroxide, such as Figure 4 and Figure 5 As shown in the figure, after the hydrogen peroxide oxidation treatment, the real dielectric part of graphene is reduced, proving that its impedance matching has been optimized to a certain extent. After modification with nickel hydroxide, the electromagnetic parameters of nickel hydroxide / graphene composites synthesized under different alkaline conditions are quite different. Combined with its micromorphology analysis, when the nickel hydroxide particles are larger, its real dielectric part and imaginary dielectric part are greatly reduced compared with the unmodified graphene sample. When the nickel hydroxide particles are smaller, its real dielectric part does not change much compared with the large particles, but its imaginary dielectric part is greatly improved, which proves that it improves the loss capacity while maintaining excellent impedance matching performance. This is because the small particles are more evenly distributed on the graphene surface, which can maximize the modification effect of nickel hydroxide on graphene.

[0037] (5) The nickel hydroxide modified graphene composite broadband electromagnetic wave absorbing material, the electromagnetic absorption mechanism of which mainly comes from the interface polarization between graphene and nickel hydroxide, the dipole polarization of nickel hydroxide itself, the dipole polarization of the surface defects of graphene oxide, combined with Figure 6 Cole curve analysis of the material. The multiple arcs shown in the figure prove the existence of multiple polarization effects in the material. These effects not only optimize the impedance matching of graphene, but also enhance the loss capacity of the material.

[0038] (6) The nickel hydroxide modified graphene composite broadband electromagnetic wave absorbing material is improved to a certain extent after the graphene is first oxidized and then modified with nickel hydroxide. Figure 6-Figure 10As shown in the figure, under the condition of sample filling ratio of 10wt% (the mass ratio of graphene composite material to paraffin is 10 to 90, which is the test requirement), the electromagnetic loss performance of pure graphene sample is poor after calculation, and there is no area with reflection loss value less than -10dB as a whole. After hydrogen peroxide oxidation treatment, it begins to appear in the frequency range of 8-12GHz near the loss value of less than -10dB, proving that the sample has good electromagnetic absorption ability in this frequency range. After nickel hydroxide modification, its effective electromagnetic wave absorption area is further expanded. For large-particle nickel hydroxide modified graphene, under the condition of sample thickness less than 2mm, its effective absorption area can cover 14-18GHz, and the effective absorption bandwidth reaches 4.0GHz. For small-particle nickel hydroxide modified graphene, under the condition of sample thickness less than 2mm, the effective absorption area can be widened to 12-18GHz, and the effective absorption bandwidth reaches 6.0GHz, achieving broadband effective absorption performance.

[0039] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0040] Example 1

[0041] The nickel hydroxide modified graphene composite broadband wave absorbing material and the preparation method thereof of the present invention comprise the following steps:

[0042] Step 1, graphene pretreatment: The pre-oxidation treatment of graphene uses hydrogen peroxide as an etchant. 1g of graphene is added to 300ml of 30wt% hydrogen peroxide solution in portions, and then 200ml of distilled water is added. After sufficient stirring, magnetic stirring is performed under a hydrothermal environment of 80℃ for 1-2 hours to separate the graphene and the solution, and the graphene is fully washed. Finally, the graphene is dried at 80℃ to obtain a graphene precursor.

[0043] Step 2: Take 100 mg of graphene precursor, add 1.12 g of nickel nitrate hexahydrate and 200 ml of distilled water, stir well and perform ultrasonic separation for 1-2 hours to obtain a precursor mixed solution.

[0044] Step 3, take 10 ml of ammonia water and 40 ml of distilled water, mix them thoroughly, and slowly pour them into the precursor mixed solution obtained in step 2. After mixing, maintain stirring for 4 hours under 100°C oil bath heating conditions, separate the solid and liquid phases in the solution, and obtain a nickel hydroxide / graphene-1 composite material sample after thorough washing and drying.

[0045] Example 2

[0046] Step 1 is the same as in Example 1.

[0047] Step 2 is the same as in Example 1.

[0048] Step 3, take 20 ml of ammonia water and 30 ml of distilled water, mix them thoroughly, and slowly pour them into the precursor mixed solution obtained in step 2. After mixing, maintain stirring for 4 hours under 100°C oil bath heating conditions, separate the solid and liquid phases in the solution, and obtain a nickel hydroxide / graphene-2 ​​composite material sample after thorough washing and drying.

[0049] Example 3

[0050] Step 1 is the same as in Example 1.

[0051] Step 2 is the same as in Example 1.

[0052] Step 3, take 30 ml of ammonia water and 20 ml of distilled water, mix them thoroughly, and slowly pour them into the precursor mixed solution obtained in step 2. After mixing, maintain stirring for 4 hours under 100°C oil bath heating conditions, separate the solid and liquid phases in the solution, and obtain a nickel hydroxide / graphene-3 composite material sample after thorough washing and drying.

[0053] Example 4

[0054] Step 1 is the same as in Example 1.

[0055] Step 2 is the same as in Example 1.

[0056] Step 3, take 40 ml of ammonia water and 10 ml of distilled water, mix them thoroughly, and slowly pour them into the precursor mixed solution obtained in step 2. After mixing, maintain stirring for 4 hours under 100°C oil bath heating conditions, separate the solid and liquid phases in the solution, and obtain a nickel hydroxide / graphene-4 composite material sample after thorough washing and drying.

[0057] Example 5

[0058] Step 1 is the same as in Example 1.

[0059] Step 2 is the same as in Example 1.

[0060] Step 3, take 50 ml of ammonia water and slowly pour it into the precursor mixed solution obtained in step 2. After mixing evenly, maintain stirring for 4 hours under 100° C. oil bath heating conditions, separate the solid and liquid phases in the solution, and obtain a nickel hydroxide / graphene-5 composite material sample after sufficient washing and drying.

[0061] Test method and sample performance analysis: The synthesized powder sample was mixed with paraffin at a ratio of 10:90 and pressed into a ring with an inner diameter of 3.04mm and an outer diameter of 7.00mm. The electromagnetic parameter test was performed using a vector network analyzer, and the reflection loss performance parameters were calculated. The results are as follows: Figure 7 , Figure 8 , Fig. 9 , Fig.10The performance of graphene raw materials is poor under this filling ratio condition. Graphene etched with hydrogen peroxide has the ability to effectively absorb electromagnetic waves under 8-12GHz conditions. The effective absorption bandwidth of the sample modified with nickel hydroxide is broadened to 6.0GHz, and its matching thickness is reduced to less than 2.0mm, which has better electromagnetic absorption performance.

[0062] It should be noted that the above-described embodiments should be understood as illustrative rather than limiting the scope of protection of the present invention, and the scope of protection of the present invention shall be subject to the claims. For those skilled in the art, some non-essential improvements and adjustments made to the present invention still fall within the scope of protection of the present invention without departing from the essence and scope of the present invention.

Claims

1. A method for preparing a nickel hydroxide modified graphene composite broadband electromagnetic wave absorbing material, characterized in that: The graphene composite broadband electromagnetic wave absorbing material is made of graphene as raw material. The graphene is first oxidized and etched to create defects on the graphene surface to generate nickel hydroxide loading sites. The nickel hydroxide is then composited with the oxidized and etched graphene to make nickel hydroxide nanoparticles evenly distributed on the graphene surface to form a nickel hydroxide modified graphene composite broadband electromagnetic wave absorbing material: It includes the following steps: Step 1, graphene pretreatment: using a 30% by mass hydrogen peroxide solution as an etchant, adding 200-300 ml of hydrogen peroxide solution to each gram of graphene raw material, and then using distilled water to prepare a total of 500 ml of a mixed solution, after being fully dispersed, heating to 60-90 degrees Celsius and maintaining the temperature for 1-2 hours, separating the graphene and the solution, and fully washing and drying to obtain a graphene precursor; Step 2: Take the graphene precursor obtained in step 1, add nickel nitrate hexahydrate, the mass ratio of nickel nitrate hexahydrate to graphene precursor is maintained at 8-13:1, add distilled water to disperse evenly, and obtain a dispersion; Step 3: Mix ammonia water and distilled water evenly, then add them to the dispersion obtained in step 2, mix evenly to obtain a reaction solution, wherein the amount of ammonia water is maintained at 4%-20% of the total volume of the reaction solution; heat the reaction solution to 90-120 degrees Celsius and maintain insulation and stirring for 4 hours, separate and wash the solid phase product after the reaction is completed, and obtain a nickel hydroxide modified graphene composite broadband electromagnetic wave absorbing material.

2. The preparation method according to claim 1, characterized in that: In step 2, distilled water is added to disperse evenly. The amount of distilled water added is adjusted according to the amount of the material to be dispersed, and the standard is that all reactants can be dispersed in the solvent.

3. The preparation method according to claim 1 and the application of the graphene composite broadband absorbing material prepared by the preparation method according to claim 1 in broadening the electromagnetic absorption band of graphene and improving electromagnetic absorption performance.

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