Preparation method for constructing graphene microwave absorbing material with directional wave absorbing characteristic

Abstract

The invention relates to a preparation method of a graphene microwave absorbing material with a directional wave absorbing characteristic, which comprises the following steps of: sequentially adding sulfuric acid with the mass concentration of 75wt%-95wt% and hydrogen peroxide with the mass concentration of 30wt%-60wt% into natural crystalline flake graphite with different sizes serving as a raw material, and standing at room temperature to obtain a graphene precursor; the graphene precursor is subjected to cleaning, vacuum filtration, stripping and freeze drying, and graphene materials with different defect behaviors are obtained. According to the method, the graphene materials with different defect behaviors are designed and prepared by regulating and controlling the mixing ratio of the sulfuric acid and the hydrogen peroxide, exciting to generate mutually competitive parallel reactions, regulating and controlling the parallel reaction rate and simultaneously coordinating the production ratio of two products, namely oxygen free radicals and bubble macromolecules, so that the time and the energy cost are saved.

Description

Technical Field

[0001] The invention relates to the technical field of graphene microwave absorbing materials, and in particular to a method for preparing a graphene microwave absorbing material with directional wave absorbing characteristics. Background Art

[0002] Since the 5G era, with the rapid development of electronic devices and wireless communications, while facilitating human life, it has also brought serious electromagnetic interference and pollution, posing a serious threat to human health and the normal operation of precision instruments. Microwave absorbing materials (MAMs) provide a promising solution by converting electromagnetic energy into heat energy for dissipation, and have been widely used in electromagnetic wave stealth, electromagnetic wave radiation protection, radar interference and wireless communications. Graphene is considered to be a promising MAMs due to its large specific surface area, low density, good mechanical properties and excellent dielectric properties.

[0003] However, the impedance mismatch caused by the high dielectric constant has always been the reason why single-component graphene materials exhibit poor microwave absorption performance, and thus cannot be the key to MAMs alone. According to the electromagnetic wave loss mechanism, adjusting the dielectric constant is crucial to enhancing impedance matching and improving the microwave absorption performance of carbon-based materials. At present, the commonly used methods to improve the dielectric constant of graphene mainly include: loading magnetic nanoparticles, constructing heterogeneous interfaces, designing hierarchical structures, etc. However, the improvement of the dielectric constant by constructing graphene-based composite materials has not fundamentally achieved the regulation of the intrinsic dielectric characteristics of graphene, and the design of the multi-component formulation process also has an adverse effect on the dispersion of the graphene absorbing material in the matrix.

[0004] Numerous studies in recent years have shown that defects are closely related to the electronic band structure, and the electronic band structure has always been a key factor in determining the dielectric constant of graphene and its derivatives. Taking advantage of the full exposure of graphene surface interface atoms to construct a multi-defect structure is considered to be the main means of regulating graphene to obtain efficient wave absorption properties. However, in recent years, with the in-depth study of graphene crystal engineering, it has been shown that new correlation mechanisms have been formed between graphene defect structures. The design of specific defect sites is related to the overall electronic structure of graphene. Therefore, the rational design of defect-functionalized coupled graphene structures is the key to constructing graphene materials with directional wave absorption properties.

[0005] So far, researchers have provided evidence that dielectric properties are closely related to electronic band structures by introducing heteroatoms to construct graphene-based composites, and based on this, have improved the dielectric properties of composites. However, there are still no reports on improving the dielectric constant of single-component graphene by constructing defects. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing a graphene microwave absorbing material with directional wave absorbing properties, which saves time and energy costs.

[0007] In order to solve the above problems, the present invention discloses a method for preparing a graphene microwave absorbing material with directional wave absorption characteristics, which is characterized in that: the method adopts natural flake graphite of different sizes as raw materials, sequentially adds sulfuric acid with a mass concentration of 75wt% to 95wt% and hydrogen peroxide with a mass concentration of 30wt% to 60wt%, and leaves the mixture to stand at room temperature to obtain a graphene precursor; the graphene precursor is washed, vacuum filtered, peeled, and freeze-dried to obtain graphene materials with different defect behaviors.

[0008] The size of the natural flake graphite is 5-50 μm.

[0009] The volume ratio of the sulfuric acid to the hydrogen peroxide is 2:1-20:1; the mass ratio of the natural flake graphite to the sulfuric acid is 1:2-20.

[0010] The standing time is 3 to 24 hours.

[0011] The cleaning refers to cleaning with one of methanol, anhydrous ethanol, acetone, and N,N-dimethylformamide until the pH value is 2-3, and then washing with water until the pH value is 7.

[0012] The stripping refers to a liquid phase mechanical stripping method.

[0013] The different defect behaviors are calculated based on the peak intensity ratio of the D peak and the G peak in the Raman spectrum. D / I G is the evaluation standard of defect level, and I D / I G It is 0.1~0.4.

[0014] Compared with the prior art, the present invention has the following advantages: 1. The present invention controls the ratio of sulfuric acid and hydrogen peroxide to stimulate competing parallel reactions, controls the parallel reaction rates, and coordinates the production ratio of oxygen free radicals and bubble macromolecules, thereby designing and preparing graphene materials with different defect behaviors.

[0015] 2. The present invention analyzes the microwave absorption frequency band and microwave absorption characteristics of graphene under different defect levels, and screens suitable graphene preparation formulas according to different microwave absorption requirements, thereby providing a solution for the material design of directional microwave absorption characteristics.

[0016] 3. The present invention directly uses graphene as raw material without subsequent processing steps, which greatly saves time and energy costs and provides a key technology for the practical and large-scale application of absorbing materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0018] Figure 1 This is the Raman map of Example 1 of the present invention.

[0019] Figure 2 This is the Raman image of Comparative Example 1 of the present invention.

[0020] Figure 3 This is the Raman map of Example 2 of the present invention.

[0021] Figure 4 This is a reflection loss-frequency diagram of Example 2 of the present invention.

[0022] Figure 5 It is a scanned image of Comparative Example 2 of the present invention.

[0023] Figure 6 This is the Raman map of Example 3 of the present invention.

[0024] Figure 7 This is a reflection loss-frequency diagram of Example 3 of the present invention.

[0025] Figure 8 This is a reflection loss-frequency diagram of comparative example 3 of the present invention. DETAILED DESCRIPTION

[0026] A preparation method of a graphene microwave absorbing material with directional wave absorption characteristics, the method is to use natural flake graphite of different sizes as raw materials, add sulfuric acid with a mass concentration of 75wt% to 95wt% and hydrogen peroxide with a mass concentration of 30wt% to 60wt% in sequence, and stand at room temperature for 3 to 24 hours to obtain a graphene precursor. At this time, the defect behavior is completed. The graphene precursor is first washed with one of methanol, anhydrous ethanol, acetone, and N,N-dimethylformamide until the pH value is 2 to 3, and then the excess acid is removed by vacuum filtration; then washed with water until the pH value is 7; then the liquid phase mechanical stripping method is used for stripping, and finally freeze-dried at -60°C for 48 hours to obtain graphene materials with different defect behaviors. Based on the differences in dielectric properties of graphene with different defects, graphene materials with different wave absorption frequency bands and performances are obtained. The removed acid can be recycled.

[0027] Among them: the size of natural flake graphite is 5~50μm.

[0028] The volume ratio (mL / mL) of sulfuric acid to hydrogen peroxide is 2:1~20:1; the mass ratio (g / g) of natural flake graphite to sulfuric acid is 1:2~20.

[0029] The equipment selected for the liquid phase high pressure process during stripping is one of a high pressure homogenizer, a high pressure emulsifying shearing machine and a micro jet homogenizer.

[0030] Different defect behaviors are calculated by the peak intensity ratio of D peak and G peak in Raman spectrum. D / I G is the evaluation standard of defect level, and I D / I G It is 0.1~0.4.

[0031] Example 1 When the graphite size is selected to be 30 μm, a defective graphene microwave absorbing material is constructed, and the specific preparation process is as follows: First, natural graphite (0.1 g) was added to H2SO4 (20 mL). The concentration of sulfuric acid was 80%. Then, H2O2 was slowly dripped into the above solution (corresponding to a volume ratio of H2SO4 to H2O2 of 5:1). The mixture was left at room temperature overnight until there was no significant change in volume. The resulting mixture was washed with methanol, vacuum filtered to remove the acid, and then washed with distilled water until the pH value of the filtrate was close to ~7. Finally, intercalated graphite was obtained after freeze drying.

[0032] The intercalated graphite was subjected to Raman analysis, and the results were as follows: Figure 1 As shown, defective intercalated graphite was successfully constructed when the graphite size was 30 μm.

[0033] Comparative Example 1 When the graphite size is selected as 70 μm, the specific preparation process of graphene microwave absorbing material is as follows: First, natural graphite (0.1 g) was added to H2SO4 (20 mL). Then, H2O2 was slowly dripped into the above solution (corresponding to a volume ratio of H2SO4 and H2O2 of 5:1). The mixture was left at room temperature overnight until there was no significant change in volume. The resulting mixture was vacuum filtered to remove the acid and then repeatedly washed with H2O until the pH of the filtrate was close to ~7. Finally, intercalated graphite was obtained after freeze drying.

[0034] The intercalated graphite was subjected to Raman analysis, and the results were as follows: Figure 2 As shown, when the graphite size is selected as 70μm, the defects are not obvious and the defect level is very low.

[0035] Example 2 The specific preparation process of graphene microwave absorbing material is as follows: First, natural graphite (30 μm, 0.1 g) was added to H2SO4 (20 mL). Then, H2O2 was slowly dripped into the above solution (the volume ratio of sulfuric acid to hydrogen peroxide was 4:1). The mixture was left at room temperature overnight until there was no significant change in volume. The resulting mixture was washed with anhydrous ethanol, vacuum filtered to remove the acid, and then washed with distilled water until the pH value of the filtrate was close to ~7. Finally, intercalated graphite was obtained after freeze drying.

[0036] The obtained intercalated graphite was subjected to Raman analysis and reflection loss analysis, and the results are as follows: Figure 3 , Figure 4 As shown, the H2SO4 content is high and the defect level is I D / I G =0.24, effective microwave absorption is achieved in the high frequency band.

[0037] Comparative Example 2 When the sulfuric acid concentration is 50%, the specific preparation process of graphene microwave absorbing material is as follows: First, natural graphite (30 μm, 0.1 g) was added to H2SO4 (20 mL). Then, H2O2 was slowly dripped into the above solution (corresponding to a volume ratio of H2SO4 to H2O2 of 5:1). The mixture was left at room temperature overnight until there was no significant change in volume. The resulting mixture was vacuum filtered to remove the acid and then repeatedly washed with H2O until the pH of the filtrate was close to ~7. Finally, intercalated graphite was obtained after freeze drying.

[0038] The obtained intercalated graphite was scanned and analyzed, and the results were as follows: Figure 5 As shown, when the sulfuric acid concentration is too low, the graphite is not exfoliated.

[0039] Example 3 The specific preparation process of graphene microwave absorbing material is as follows: First, natural graphite (30 μm, 0.1 g) was added to H2SO4 (20 mL). Then, H2O2 was slowly dripped into the above solution (the volume ratio of sulfuric acid to hydrogen peroxide was 10:1). The mixture was left at room temperature overnight until there was no significant change in volume. The resulting mixture was washed with acetone, vacuum filtered to remove the acid, and then washed with distilled water until the pH value of the filtrate was close to ~7. Finally, intercalated graphite was obtained after freeze drying.

[0040] The obtained intercalated graphite was subjected to Raman analysis and reflection loss analysis, and the results are as follows: Figure 6 , Figure 7 As shown, the H2SO4 content is high and the defect level is I D / I G=0.31, effective microwave absorption is achieved in the high frequency band.

[0041] Comparative Example 3 The specific preparation process of graphene microwave absorbing material is as follows: First, natural graphite (30 μm, 0.1 g) was added to H2SO4 (20 mL). Then, H2O2 was slowly dripped into the above solution (the volume ratio of sulfuric acid to hydrogen peroxide was 1:1). The mixture was left at room temperature overnight until there was no significant change in volume. The resulting mixture was vacuum filtered to remove the acid and then repeatedly washed with H2O until the pH of the filtrate was close to ~7. Finally, intercalated graphite was obtained after freeze drying.

[0042] The reflection loss analysis of the obtained intercalated graphite is shown in the following results: Figure 8 As shown, when the sulfuric acid content is too high, effective absorption cannot be carried out.

Claims

1. A method for preparing a graphene microwave absorbing material with directional microwave absorption characteristics, characterized in that: The method comprises the following steps: using natural flake graphite of different sizes as raw materials, sequentially adding sulfuric acid with a mass concentration of 75wt% to 95wt% and hydrogen peroxide with a mass concentration of 30wt% to 60wt%, and standing the mixture at room temperature to obtain a graphene precursor; and the graphene precursor is washed, vacuum filtered, peeled, and freeze-dried to obtain graphene materials with different defect behaviors.

2. The method for preparing a graphene microwave absorbing material with directional microwave absorption characteristics as claimed in claim 1, characterized in that: The size of the natural flake graphite is 5-50 μm.

3. The method for preparing a graphene microwave absorbing material with directional microwave absorption characteristics as claimed in claim 1, characterized in that: The volume ratio of the sulfuric acid to the hydrogen peroxide is 2:1-20:1; the mass ratio of the natural flake graphite to the sulfuric acid is 1:2-20.

4. The method for preparing a graphene microwave absorbing material with directional microwave absorption characteristics as claimed in claim 1, characterized in that: The standing time is 3 to 24 hours.

5. The method for preparing a graphene microwave absorbing material with directional microwave absorption characteristics as claimed in claim 1, characterized in that: The cleaning refers to cleaning with one of methanol, anhydrous ethanol, acetone, and N,N-dimethylformamide until the pH value is 2-3, and then washing with water until the pH value is 7.

6. The method for preparing a graphene microwave absorbing material with directional microwave absorption characteristics as claimed in claim 1, characterized in that: The stripping refers to a liquid phase mechanical stripping method.

7. The method for preparing a graphene microwave absorbing material with directional microwave absorption characteristics as claimed in claim 1, characterized in that: The different defect behaviors are calculated based on the peak intensity ratio of the D peak and the G peak in the Raman spectrum. D / I G is the evaluation standard of defect level, and I D / I G It is 0.1~0.4.

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