Preparation and Application of Fe3O4@CGFA Composite Material

Abstract

The present invention discloses the preparation and application of Fe<subgt;3< / subgt>O<subgt;4< / subgt>@CGFA composite materials. The method steps for preparing the composite materials are as follows: S1: Acidification of CGFA; S2: Synthesis of Fe<subgt;3< / subgt>O<subgt;4< / subgt>@CGFA; S21: Add the acidified CGFA and polyvinylpyrrolidone in S1 into distilled water, stir and mix evenly, and then heat up to 55 - 65 °C; S22: Dissolve FeCl<subgt;3< / subgt>·6H<subgt;2< / subgt>O and FeCl<subgt;2< / subgt>·4H<subgt;2< / subgt>O in deionized water respectively and mix evenly; S23: Add the FeCl<subgt;3·6H<subgt;2O and FeCl<subgt;2·4H<subgt;2O solutions in S22 into the mixture in S21, and stir for 12 - 18 min; S24: Add concentrated ammonia water to the mixture in S23, and stir for 1.8 - 2.2 h, controlling the pH of the mixture to be 10; S25: After the reaction is completed, magnetize the prepared product, wash it with deionized water and absolute ethanol until neutral, and obtain Fe<subgt;3O<subgt;4@CGFA after drying. The composite materials prepared by the present invention have good electromagnetic wave absorption performance, thus promoting the resource utilization of coal gasification solid waste.

Description

Technical Field

[0001] The present invention relates to the technical field of composite materials, and particularly to the preparation and application of Fe3O4@CGFA composite materials. Background Art

[0002] With the wide application of electronic information technology in industries, commerce, military and other fields, wireless devices play an important role in people's daily lives. However, the electromagnetic pollution and electromagnetic interference generated by electronic and electrical devices have a great impact on people's lives and work. Therefore, it is urgent to develop electromagnetic wave absorbing materials with excellent performance. Carbon materials have become one of the most important non-metallic materials due to their large specific surface area, good chemical stability, high mechanical strength and low density. They have been widely used in fields such as purification, batteries, catalysis, desulfurization, especially microwave absorption. Carbon materials belong to the type of dielectric loss absorption materials and have strong research hotspots, such as graphene. The microwave absorption properties of GN, carbon nanofibers, carbon nanofibers, CNFs, carbon black (CB), carbon nanotubes, carbon nanotubes and their composites have received extensive attention and research.

[0003] As a promising clean coal technology, coal gasification has made great progress in China in recent years. And the pulverized coal gasification technology has become one of the mainstream technologies in the field of coal gasification (which is considered to be more effective due to its strong coal type adaptability, high carbon conversion rate and low operating cost). During the coal gasification process, some inorganic components and a small amount of unreacted carbon will form fly ash or coal gasification ash (CGFA). CGFA is an inevitable by-product during the coal gasification process, usually piled up in the open air, occupying a large area, with low utilization rate, and may cause pollution to soil, air, water, etc. The residual carbon content of CGFA reaches 60%, which can be used as a potential source of carbon-based materials. And how to prepare materials with high microwave absorption performance from CGFA remains to be further studied. Summary of the Invention

[0004] Based on the technical problems existing in the background art, the present invention proposes the preparation and application of Fe3O4@CGFA composite materials. The prepared composite materials have good electromagnetic wave absorption performance, thus promoting the resource utilization of coal gasification solid waste.

[0005] The method steps for preparing the Fe3O4@CGFA composite materials proposed by the present invention are as follows:

[0006] S1: Acidification of CGFA

[0007] S2: Synthesis of Fe3O4@CGFA

[0008] S21: Add the acidified CGFA and polyvinylpyrrolidone in S1 into distilled water, stir and mix evenly, and then heat up to 55 - 65°C;

[0009] S22: Dissolve FeCl3·6H2O and FeCl2·4H2O separately in deionized water and mix them evenly;

[0010] S23: Add the FeCl3·6H2O and FeCl2·4H2O solutions in S22 to the mixed solution in S21, and stir for 12 - 18 min;

[0011] S24: Add concentrated ammonia water to the mixed solution in S23, and stir for 1.8 - 2.2 h, controlling the pH of the mixed solution to be 10;

[0012] S25: After the reaction, magnetize the prepared product, wash it with deionized water and absolute ethanol until neutral, and dry it to obtain Fe3O4@CGFA.

[0013] Preferably, the method steps for acidifying CGFA in S1 are as follows:

[0014] S11: Add hydrochloric acid solution to the container containing CGFA, and stir and react at 105 °C for 1.8 - 2.2 h;

[0015] S12: Filter the mixed solution in S11, wash the remaining solid with deionized water until neutral, and dry it;

[0016] S13: Add hydrofluoric acid solution to the container containing the dried solid particles in S12, and stir and react at 105 °C for 1.8 - 2.2 h;

[0017] S14: Filter the mixed solution in S13, wash the remaining solid with deionized water until neutral, and dry it;

[0018] S15: Add hydrochloric acid solution to the container containing the dried solid particles in S14, and stir and react at 105 °C for 1.8 - 2.2 h;

[0019] S16: Filter the mixed solution in S11, wash the remaining solid with deionized water until neutral, and dry it to obtain acidified CGFA.

[0020] Preferably, the drying conditions in S12, S14, and S16 are a temperature of 100 - 110 °C and a time of 10 - 14 h.

[0021] Preferably, the concentration of the hydrochloric acid solution in S11 is 5 mol / L, and the mass - volume ratio of the gasification fine slag to the hydrochloric acid solution is 1 g:8 - 12 mL.

[0022] Preferably, the mass fraction of the hydrofluoric acid solution in S13 is 40%, and the mass - volume ratio of the gasification fine slag to the hydrofluoric acid solution is 1 g:8 - 12 mL.

[0023] Preferably, in S15, the concentration of the hydrochloric acid solution is 1.19 g / mL, and the mass-to-volume ratio of the gasified fine slag to the hydrochloric acid solution is 1 g: 8 - 12 mL.

[0024] Preferably, the mass ratio of the CGFA, polyvinylpyrrolidone, deionized water, FeCl3·6H2O, and FeCl2·4H2O is 1: 0.4 - 0.6: 80 - 85: 0.1 - 0.5: 0.5 - 1.5.

[0025] Preferably, the drying conditions in S25 are: drying under vacuum at 55 - 65 °C for 10 - 14 h.

[0026] The Fe3O4@CGFA composite material prepared by the above method proposed by the present invention.

[0027] The application of the Fe3O4@CGFA composite material proposed by the present invention in electromagnetic wave absorption.

[0028] Compared with the prior art, the beneficial technical effects of the present invention:

[0029] The Fe3O4@CGFA composite material prepared by the present invention by compounding CGFA with iron ions has excellent electromagnetic parameters and electromagnetic wave absorption performance. The Fe3O4@CGFA composite material prepared in Example 2, at a thickness of 1.5 mm, the minimum reflection loss (RL min ) value can reach -37.4 dB, the effective absorption bandwidth (RL ≤ 10 dB) is 4.16 GHz (13.84 - 18 GHz), and the impedance matching is 1.00. The Fe3O4@CGFA product prepared in Example 3, when the thickness of the absorption layer is only 2.0 mm, the minimum reflection loss (RL min ) value can reach -41.4 B, and the effective absorption bandwidth (RL ≤ 10 dB) is 4.32 GHz (13.68 - 18 GHz). The Fe3O4@CGFA composite materials prepared in Examples 2 and 3 both show high-performance energy absorption in the microwave band. After loading magnetic particles on the surface of CGFA, the composite material shows excellent microwave absorption performance. Therefore, CGFA can replace graphite as an excellent microwave absorption material. This research provides an effective direction for the high-value utilization of coal gasification fine ash. Description of the Drawings

[0030] Figure 1 In (a) and (b) are respectively the XRD pattern and the TGA curve of the Fe3O4@CGFA composite material;

[0031] Figure 2Figures (a-c) are SEM images of the Fe3O4@CGFA composites prepared in Examples 1-3, respectively; (d) is the EDX mapping image of the Fe3O4@CGFA composite prepared in Example 2.

[0032] Figure 3 is the transmission electron microscope image of the Fe3O4@CGFA composite.

[0033] Figure 4 is the XPS spectrum of the Fe3O4@CGFA composite prepared in Example 2, where (a) is the total spectrum of CGFA and Fe3O4@CGFA, (b) is the Fe 2p spectrum of Fe3O4@CGFA, (c) is the O1s spectrum of Fe3O4@CGFA, (d) is the C1s spectrum of Fe3O4@CGFA, (e) is the O1s spectrum of CGFA, and (f) is the C1s spectrum of CGFA.

[0034] Figure 5 are the electromagnetic parameters of the Fe3O4@CGFA composite proposed by the present invention: (a) real part of complex permittivity (ε′), (b) imaginary part of complex permittivity (ε″), (c) real part of complex permeability (μ′), (d) imaginary part of complex permeability (μ″), (e) tangent value of complex permittivity, and (f) tangent value of complex permeability.

[0035] Figure 6 are the 2D and 3D reflection loss curves of the Fe3O4@CGFA composite proposed by the present invention, where (a, b) are the 2D and 3D reflection loss curves of sample S1, respectively, (c, d) are the 2D and 3D reflection loss curves of sample S2, (e, f) are the 2D and 3D reflection loss curves of sample S3, (g) is the minimum reflection loss of samples S1, S2, and S3 at a thickness of 1.5 mm, and (h) is the effective absorption bandwidth (RL≤10 dB) of samples S1, S2, and S3 at a thickness of 1.5 mm.

[0036] Figure 7 [[ID=2,0]]are the triple graphs of reflection loss, λ / 4 model, and impedance matching of the Fe3O4@CGFA composite proposed by the present invention, where (a) is the triple graph of reflection loss, λ / 4 model, and impedance matching of sample S2, and (b) is the triple graph of reflection loss, λ / 4 model, and impedance matching of sample S3. Detailed implementation manners

[0037] The present invention will be further explained below in conjunction with specific embodiments.

[0038] Main instruments: X-ray diffractometer (LabX xrd-6000, Shimadzu Corporation, Japan), laser confocal Raman spectrometer (Renishaw-2000, Renishaw plc, UK), X-ray photoelectron spectrometer (ESCALAB MK, Thermo Fisher Scientific, USA), field emission scanning electron microscope (FEI Quanta 200, FEI Company, Netherlands), transmission electron microscope (JEOL-2010, JEOL Ltd., Japan), vector network analyzer (AV3629D, CETC 41st Research Institute, China).

[0039] Example 1

[0040] The method for preparing the Fe3O4@CGFA composite material proposed by the present invention is as follows:

[0041] S1: Acidification of CGFA

[0042] S11: Add 500 mL of hydrochloric acid solution (5 mol / L) to a container containing 50 g of CGFA, and stir and react at 105 °C for 1.8 h;

[0043] S12: Filter the mixture in S11, wash the remaining solid with deionized water until neutral, and dry it at 105 °C for 12 h;

[0044] S13: Add 500 mL of hydrofluoric acid solution (40% wt%) to a container containing the dried solid particles in S12, and stir and react at 105 °C for 1.8 h;

[0045] S14: Filter the mixture in S13, wash the remaining solid with deionized water until neutral, and dry it at 105 °C for 12 h;

[0046] S15: Add 500 ml of hydrochloric acid solution (1.19 g / mL) to a container containing the dried solid particles in S14, and stir and react at 105 °C for 1.8 h;

[0047] S16: Filter the mixture in S11, wash the remaining solid with deionized water until neutral, and dry it at 105 °C for 12 h to obtain acidified CGFA.

[0048] S2: Synthesis of Fe3O4@CGFA

[0049] S21: Add 0.6 g of acidified CGFA and 0.3 g of polyvinylpyrrolidone in S1 to 50 mL of distilled water, stir and mix well, and then heat to 60 °C;

[0050] S22: Dissolve 0.1 g of FeCl3·6H2O and 0.3 g of FeCl2·4H2O in 50 mL of deionized water respectively and mix them evenly;

[0051] S23: Add the FeCl3·6H2O and FeCl2·4H2O solutions in S22 to the mixed solution in S21, and stir for 15 min;

[0052] S24: Add concentrated ammonia water to the mixed solution in S23, and stir for 2 h, controlling the pH of the mixed solution to be 10;

[0053] S25: Magnetize the prepared product after the reaction, wash it with deionized water and absolute ethanol until neutral, and obtain Fe3O4@CGFA after drying, denoted as S1.

[0054] Example 2

[0055] The method for preparing the Fe3O4@CGFA composite material proposed by the present invention is as follows:

[0056] S1: Acidification of CGFA

[0057] S11: Add 500 mL of hydrochloric acid solution (5 mol / L) to the container containing 50 g of CGFA, and stir and react at 105 °C for 1.8 h;

[0058] S12: Filter the mixed solution in S11, wash the remaining solid with deionized water until neutral, and dry it at 105 °C for 12 h;

[0059] S13: Add 500 mL of hydrofluoric acid solution (40% wt%) to the container containing the dried solid particles in S12, and stir and react at 105 °C for 1.8 h;

[0060] S14: Filter the mixed solution in S13, wash the remaining solid with deionized water until neutral, and dry it at 105 °C for 12 h;

[0061] S15: Add 500 ml of hydrochloric acid solution (1.19 g / mL) to the container containing the dried solid particles in S14, and stir and react at 105 °C for 1.8 h;

[0062] S16: Filter the mixed solution in S11, wash the remaining solid with deionized water until neutral, and dry it at 105 °C for 12 h to obtain acidified CGFA.

[0063] S2: Synthesis of Fe3O4@CGFA

[0064] S21: Add 0.6 g of acidified CGFA and 0.3 g of polyvinylpyrrolidone in S1 into 50 mL of distilled water, stir and mix evenly, and then heat up to 60 °C;

[0065] S22: Dissolve 0.2 g of FeCl3·6H2O and 0.6 g of FeCl2·4H2O in 50 mL of deionized water respectively and mix evenly;

[0066] S23: Add the FeCl3·6H2O and FeCl2·4H2O solutions in S22 into the mixture in S21, and stir for 15 min;

[0067] S24: Add concentrated ammonia water into the mixture in S23, and stir for 2 h, controlling the pH of the mixture to be 10;

[0068] S25: Magnetize the prepared product after the reaction, wash it with deionized water and absolute ethanol until neutral, and obtain Fe3O4@CGFA after drying, denoted as S2.

[0069] Example 3

[0070] The steps of the method for preparing the Fe3O4@CGFA composite material proposed by the present invention are as follows:

[0071] S1: Acidification of CGFA

[0072] S11: Add 500 mL of hydrochloric acid solution (5 mol / L) to the container containing 50 g of CGFA, and stir and react at 105 °C for 1.8 h;

[0073] S12: Filter the mixture in S11, wash the remaining solid with deionized water until neutral, and dry it at 105 °C for 12 h;

[0074] S13: Add 500 mL of hydrofluoric acid solution (40% wt%) to the container containing the dried solid particles in S12, and stir and react at 105 °C for 1.8 h;

[0075] S14: Filter the mixture in S13, wash the remaining solid with deionized water until neutral, and dry it at 105 °C for 12 h;

[0076] S15: Add 500 ml of hydrochloric acid solution (1.19 g / mL) to the container containing the dried solid particles in S14, and stir and react at 105 °C for 1.8 h;

[0077] S16: Filter the mixture in S11, wash the remaining solid with deionized water until neutral, and dry it at 105 °C for 12 h to obtain acidified CGFA.

[0078] S2: Synthesis of Fe3O4@CGFA

[0079] S21: Add 0.6 g of acidified CGFA and 0.3 g of polyvinylpyrrolidone in S1 into 50 mL of distilled water, stir and mix well, then heat up to 60 °C;

[0080] S22: Dissolve 0.3 g of FeCl3·6H2O and 0.9 g of FeCl2·4H2O in 50 mL of deionized water respectively and mix well;

[0081] S23: Add the FeCl3·6H2O and FeCl2·4H2O solutions in S22 into the mixture in S21, and stir for 15 min;

[0082] S24: Add concentrated ammonia water into the mixture in S23, and stir for 2 h, controlling the pH of the mixture to be 10;

[0083] S25: After the reaction is completed, magnetize the prepared product, wash it with deionized water and absolute ethanol until neutral, and dry it to obtain Fe3O4@CGFA, denoted as S3.

[0084] In the synthesis process of the Fe3O4@CGFA composite material, Fe 2+ and Fe 3+ ions are first attracted by the defects and electron-negative functional groups of CGFA through strong electrostatic interaction, then ammonia water is added as a precipitating agent to generate iron hydroxide, and the iron hydroxide stays on the surface of CGFA. After the solvothermal reaction accompanied by grain crystallization and growth, the self-assembled Fe3O4 particles are wrapped by CGFA to form the final Fe3O4@CGFA composite material.

[0085] Refer to Figure 1 , and use XRD to analyze the crystal structure of the composite materials prepared in Examples 1-3. As shown in (a) of Figure 1 , the diffraction peaks of each sample are at 2θ = 30.12°, 35.53°, 43.18°, 53.73°, 57.26° and 62.73° respectively, which are in good agreement with the (220), (311), (400), (422), (511) and (440) planes of Fe3O4 (JCPDS card NO.1). It shows that Fe3O4 has been successfully synthesized in the Fe3O4@CGFA composite material. CGFA shows a sharp characteristic peak (002) of graphite at 2θ = 25.8° (JCPDS card 75-2078), indicating that the carbon in coal is converted into graphitized carbon after gasification. It should be noted that with the increase of the iron oxide load, the intensity of the (002) plane becomes weaker. Figure 1The TGA curves in (b) show that the weight loss of CGFA and Fe3O4@CGFA starts from 460 °C and 360 °C respectively, and the maximum temperatures of weight loss of CGFA, S1, S2 and S3 are 985 °C, 935 °C, 830 °C and 795 °C respectively, indicating that the loading of Fe3O4 particles on CGFA has a certain catalytic combustion effect. The maximum weight loss of CGFA, S1, S2 and S3 at 1000 °C are 98.9%, 79.4%, 66.0% and 59.0% respectively. By calculating the total weight loss of the samples at 1000 °C and the remaining weight of CGFA, the Fe3O4 contents in S1, S2 and S3 are determined to be 19.5%, 32.9% and 39.9% respectively.

[0086] The micro-morphologies of the Fe3O4@CGFA nanocomposites prepared in Examples 1-3 were characterized by SEM. The Fe3O4@CGFA nanocomposites ( Figure 2 (a-c) are in irregular sheet shapes, and the slightly aggregated Fe3O4 nanoparticles are evenly distributed on the surface of CGFA, which can enrich the surface area. The corresponding element mapping images of sample S2 are as Figure 2 (d) shown. The results show that the carbon, oxygen and iron elements are evenly distributed in the composite material. The images of iron and oxygen show that these elements are well distributed on the CGFA flakes, and their position distributions have a good corresponding relationship.

[0087] The surface morphologies of samples S1 (a-c), S2 (d-f) and S3 (g-i) were studied by transmission electron microscopy, as Figure 3 shown. The surface of CGFA is covered with a large number of Fe3O4 nanoparticles, and their average size is about 30 nm. From Figure 3 (a) and (b), (d) and (e), (g) and (h), it can be clearly observed that the Fe3O4 nanoparticles are distributed on the surface of the thin-layered CGFA in the shape, but some Fe3O4 nanoparticles will agglomerate. It should be noted that with the increase of the iron content, the generated Fe3O4 nanoparticles gradually increase, and the degree of agglomeration becomes more and more serious. The HRTEM images ( Figure 3 (c), (f) and (i)) clearly show that the interplanar spacings of 0.29 nm and 0.24 nm are consistent with the (220) plane and (311) plane of Fe3O4. On this basis, the Fe3O4@CGFA with a clear disc-like morphology is beneficial to improving the electrochemical performance of electromagnetic wave absorbing materials.

[0088] In order to further determine the element valence and chemical composition of CGFA and Fe3O4@CGFA, taking sample S2 as an example, XPS determination was carried out. From Figure 4As can be seen from (a), the total spectrogram verifies the presence of C, O in CGFA and C, O, and Fe in Fe3O4@CGFA, indicating a high purity of the synthesized product. Figure 4 The Fe 2p3 / 2 energy spectrum in (b) can be fitted with three distinct peaks at 709.8, 711.4, and 713.1 eV, corresponding to Fe 2+ and Fe 3+ . The calculated ratio of Fe 3+ / Fe 2+ is 1.84. As can be seen from Figure 4 (c), the O 1s spectrum is divided into two main peaks at 530.5 eV and 532.0 eV, confirming the formation of Fe3O4 and the presence of -OH. Figure 4 (d) shows the C 1s spectrum of the Fe3O4@CGFA composite material. The peaks with binding energies of 284.4 eV, 285.6 eV, 287.0 eV, and 290.2 eV originate from C-C / C═C, C-O, O-C═O, and ring-forming π-π* bonds, respectively. This indicates the presence of oxygen-related functional groups on the surface of CGFA. Table 1 shows the weight percentages and atomic percentages of the CGFA and Fe3O4@CGFA materials. According to the O / C weight ratio and atomic ratio of CGFA are 0.074 and 0.063, respectively, while the O / C weight ratio and atomic ratio of Fe3O4@CGFA increase to 0.332 and 0.249, respectively, due to the successful loading of Fe3O4. In summary, the XPS results reveal the coexistence of Fe 3+ , Fe 2+ , O, and C in the Fe3O4@CGFA composite material.

[0089] Table 1 Weight percentages and atomic percentages of CGFA and Fe3O4@CGFA

[0090]

[0091] Generally speaking, the EMW absorption behavior of the absorber mainly depends on the electromagnetic parameters (ε′, ε″, μ′, and μ″). The imaginary parts (ε″, μ″) represent magnetic loss or dielectric loss, respectively, and the real parts (ε′, μ′) are related to the stored magnetic energy or electrical energy, respectively. Figure 5 (a)-(d) describe the electromagnetic parameters of the synthesized Fe3O4@CGFA nanocomposite as a function of frequency. As Figure 5 shown in (a), as the frequency increases, the ε′ of the Fe3O4@CGFA nanocomposite shows a gradually decreasing trend, exhibiting frequency dispersion behavior, which is conducive to the attenuation of electromagnetic energy. In addition, as the iron content increases, ε′ gradually decreases, which is related to the low carbon content. From Figure 5As can be seen from (b) of, the ε″ of the synthesized nanocomposites shows a similar trend. The value of specimen S1 is the largest in the whole frequency range, which can be attributed to its high conductivity. Figure 5 (c) and (d) describe the μ′ and μ″ vs. frequency curves of the Fe3O4@CGFA nanocomposites. The values of μ′ and μ″ show a downward trend. In addition, the values of μ″ are negative within 818 GHz, indicating the existence of radiation phenomenon. To compare the dielectric loss performance, we plotted the curve of dielectric loss tangent (tanε = ε″ / ε′)) vs. frequency, as Figure 5 shown in (e) of. Dielectric loss mainly comes from polarization loss and conduction loss. Polarization loss includes electrical, ionic, dipolar and interfacial polarization losses, while conduction loss mainly comes from conductivity loss. In particular, the curves of tanε vs. frequency of specimen S1 and specimen S2 are similar, while specimen S2 shows different trends at 6 - 10 GHz, indicating that the loading content affects the dielectric loss ability of the Fe3O4@CGFA nanocomposites to a certain extent. To study the magnetic loss performance, the curve of magnetic loss tangent (tanμ = μ″ / μ') vs. frequency was plotted. Figure 5 The curves of tan μ vs. frequency of the three specimens in (f) of are similar to the variation trend of μ″. In addition, the tanε of the Fe3O4 / CGFA nanocomposites with different Fe3O4 loadings is significantly greater than tanμ. This indicates that dielectric loss is the main mechanism for the attenuation of electromagnetic energy in the nanocomposites.

[0092] To investigate the effect of the addition amount of Fe3O4 on the EMW absorption behavior of the prepared Fe3O4@CGFA nanocomposites, the 2D and 3D RL - frequency curves of Fe3O4@CGFA with a thickness of 1.5 - 5.0 mm in the range of 2 - 18 GHz were plotted. It should be noted that specimen S3 shows the best EMW absorption behavior compared with the other two specimens ( Figure 6 (e), (f) of), that is, the RL min is - 41.4 dB at 2.0 mm. When the thickness is 1.5 mm, the maximum EAB can reach 4.32 GHz. As Figure 6 shown in (a), (b) of, specimen S1 shows poor EMW absorption behavior, that is, when the thickness is 1.5 mm, its RL min is - 9.6 dB at 11.92 GHz. As can be seen from Figure 6 (c), (d) of, the EMW absorption ability of specimen S2 is better. When the thickness is 1.5 mm, the RL min is - 37.3 dB, and the maximum EAB can reach 4.16 GHz (18 - 13.84 GHz), which can achieve absorption in almost all Ku - bands (12 - 18 GHz). To more intuitively see the variation of RL and EAB with the specimens,Figure 6 (g) and (h) respectively give the |RLmin| and EAB-Fe3O4@CGFA curves and histograms. With the increase of the Fe3O4 addition amount, the |RLmin| value shows a trend of increasing first and then decreasing when the thickness is 1.5 mm. The EAB of specimens S2 and S3 are both greater than 4. In summary, compared with specimen S1, specimens S2 and S3 show good EMW absorption behavior, indicating that a certain amount of Fe3O4 loading can effectively improve the EMW absorption ability.

[0093] To effectively absorb electromagnetic waves, the absorbing or absorbing structural material should meet the following requirements: The electromagnetic wave incident surface of the material can completely enter its interior, reducing the surface reflection to the greatest extent, which is called the impedance matching characteristic of the material. Therefore, the impedance matching mechanism can be studied according to the impedance matching characteristic (Z) and the fitting λ / 4 wavelength matching model. An ideal absorber should exhibit zero reflection and a target of 1.0, indicating that all waves can enter the absorber without reflection. Therefore, when the calculated value of Z is close to 1, the impedance matching degree is better and the microwave absorption performance is stronger. And the frequency point corresponding to the peak of the reflection loss curve is matched with the wavelength matching model. Figure 7 The impedance matching characteristics of two different thickness composites at 2 - 18 GHz and the microwave / 4 wavelength matching model with different thicknesses are given. It can be seen that with the increase of the thickness, the frequency points corresponding to the peaks of the reflection loss curves of specimens S1, S2, and S3 shift to the low frequency, and the results are consistent with the mr / 4 wavelength matching model. When the thickness is 1.5 mm and 2.0 mm, the Z values of specimen S2 are 1.00 and 1.12 respectively, and when the thickness is 1.5 mm and 2.0 mm, the Z values of specimen S3 are 0.90 and 0.98 respectively, proving that the composites of specimens S2 and S3 have good impedance matching.

[0094] As described above, it is only the preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all should be covered by the protection scope of the present invention.

Claims

1. Preparation method of Fe3O4@CGFA composite material, characterized in that, The method steps are as follows: S1: Acidification of CGFA; S2: Synthesis of Fe3O4@CGFA; S21: Add the acidified CGFA and polyvinylpyrrolidone in S1 to distilled water, stir and mix evenly, and then heat up to 55 - 65 °C; S22: Dissolve FeCl3·6H2O and FeCl2·4H2O in deionized water respectively and mix evenly; S23: Add the FeCl3·6H2O and FeCl2·4H2O solutions in S22 to the mixture in S21, and stir for 12 - 18 min; S24: Add concentrated ammonia water to the mixture in S23, and stir for 1.8 - 2.2 h, controlling the pH of the mixture to be 10; S25: After the reaction, magnetize the prepared product, wash it with deionized water and absolute ethanol until neutral, and dry it to obtain Fe3O4@CGFA; The method steps of the acidification of CGFA in S1 are as follows: S11: Add hydrochloric acid solution to the container containing CGFA, and stir and react at 105 °C for 1.8 - 2.2 h; S12: Filter the mixture in S11, wash the remaining solid with deionized water until neutral, and dry it; S13: Add hydrofluoric acid solution to the container containing the dried solid particles in S12, and stir and react at 105 °C for 1.8 - 2.2 h; S14: Filter the mixture in S13, wash the remaining solid with deionized water until neutral, and dry it; S15: Add hydrochloric acid solution to the container containing the dried solid particles in S14, and stir and react at 105 °C for 1.8 - 2.2 h; S16: Filter the mixture in S11, wash the remaining solid with deionized water until neutral, and dry it to obtain acidified CGFA; The Fe3O4@CGFA composite material has a clear disc - like morphology.

2. The preparation method of the Fe3O4@CGFA composite material according to claim 1, characterized in that, The drying conditions in S12, S14, and S16 are a temperature of 100 - 110 °C and a time of 10 - 14 h.

3. The preparation method of the Fe3O4@CGFA composite material according to claim 1, characterized in that, The concentration of the hydrochloric acid solution in S11 is 5 mol / L, and the mass - to - volume ratio of CGFA to the hydrochloric acid solution in S11 is 1 g:8 - 12 mL.

4. The preparation method of the Fe3O4@CGFA composite material according to claim 1, characterized in that, The mass fraction of the hydrofluoric acid solution in S13 is 40%, and the mass - to - volume ratio of the dried solid particles in S12 to the hydrofluoric acid solution is 1 g:8 - 12 mL.

5. The preparation method of the Fe3O4@CGFA composite material according to claim 1, characterized in that, The concentration of the hydrochloric acid solution in S15 is 1.19 g / mL, and the mass - to - volume ratio of the dried solid particles in S14 to the hydrochloric acid solution is 1 g:8 - 12 mL.

6. The preparation method of the Fe3O4@CGFA composite material according to claim 1, characterized in that, The mass ratio of CGFA, polyvinylpyrrolidone, deionized water, FeCl3·6H2O, and FeCl2·4H2O is 1:0.4 - 0.6:80 - 85:0.1 - 0.5:

7. The preparation method of the Fe3O4@CGFA composite material according to claim 1, characterized in that, ​ ​ ​

Images