Al-MOF-derived CAU-Al (200, 300) / rGO composite wave-absorbing material and preparation method thereof

Abstract

The invention belongs to the technical field of electromagnetic wave absorbing materials, and relates to an Al-MOF-derived CAU-Al / rGO composite wave absorbing material and a preparation method thereof. The composite material takes a CAU-10-H (Al) MOF carbon-based derivative and reduced graphene oxide as main components, and is prepared through the processes of a solvothermal method, water bath heating, heat treatment, freeze drying and the like. The preparation method comprises the following steps: mixing graphite oxide powder and an ascorbic acid reducing agent according to a mass ratio, and carrying out stirring, cell crushing, a hydrothermal method and a vacuum freeze drying method so as to obtain reduced graphene oxide black powder; then, the CAU-10-H (Al) precursor is placed in a tubular furnace, and the CAU-Al (200) and the CAU-Al (300) are formed through heating and carbonization in the argon atmosphere; and finally, mixing the CAU-Al and the reduced graphene oxide powder according to a mass ratio, and uniformly stirring to obtain the composite wave-absorbing material. The carbonized MOF particles are doped in the reduced graphene oxide, so that the characteristic of light weight is realized, the dielectric loss capability, interface polarization and relaxation loss of the composite material are improved, the composite material has good impedance matching with air, and the electromagnetic wave absorption performance is remarkably enhanced.

Description

Technical Field

[0001] The present invention belongs to the technical field of electromagnetic wave absorption materials, and more specifically relates to a preparation method of a composite material derived from MOF as a precursor, and its application development in the field of electromagnetic wave absorption. Background Art

[0002] With the rapid development of science and technology and innovative functional materials, efficient and stable electromagnetic functional materials can not only combat the increasing electromagnetic pollution problem, but also have wide applications in military, information and other fields. High-performance microwave absorption materials have the advantages of low density and thin thickness, and have an effective frequency bandwidth and the ability to attenuate electromagnetic waves, which can eliminate the adverse effects of electromagnetic waves on human health, electronic devices and military security, etc.

[0003] Among them, the metal-organic framework MOF (Metal Organic Framework) derived material is a new type of wave-absorbing material, which has the characteristics of simple synthesis process, low production cost, good thermal stability, large specific surface area, high porosity, etc. MOF materials have a highly adjustable microstructure and composition. Among them, CAU-10-H with a cubic molecular structure is a new type of MOF, which is very rare in the reports of wave-absorbing materials. In recent years, Al-based MOF has attracted extensive attention because of its low price, low toxicity, high chemical stability and high thermal stability.

[0004] Graphene has a very high specific surface area and ideal microwave absorption characteristics, and can be used to prepare microwave absorption materials with low density and strong plasticity, which can have the characteristics of a limited frequency bandwidth in microwave absorption materials. Although the conductivity of MOF is low, graphene, which has been reported a lot in recent years, has relatively stable conductivity. However, as a material with a relatively high conductivity, graphene still has the disadvantages of poor impedance matching and poor attenuation loss as a wave-absorbing material. Therefore, graphene is combined with other dielectric loss materials or magnetic loss materials to increase interfacial polarization and reduce material loss.

[0005] In microwave absorption materials, using metal-organic framework MOF as a precursor has the characteristics of preparing magnetic particles, porous carbon, metal compounds and derived composite materials, etc., and has superior conductivity, good magnetism, and multiple interfaces, which have obvious advantages in impedance matching and microwave loss. And graphene, as a new type of carbon material, with its unique two-dimensional structure and adjustable large specific surface area, is widely used in electromagnetic wave absorption.

[0006] Reference 1 "Huang, X., Wei, J., Zhang, Y., Qian, B., Jia, Q., Liu, J., Shao, G. Ultralight Magnetic and Dielectric Aerogels Achieved by Metal-Organic Framework Initiated Gelation of Graphene Oxide for Enhanced Microwave Absorption. Nano-Micro Letters, 14 (2022) 014-007." reported the preparation methods of Fe3O4@C / rGO and Ni-doped Fe3O4@C / rGO aerogels. The gelation mechanism eliminated the electrostatic repulsion of the connection sites provided by the free metal ions on the surface of MIL-88A nanorods, and assembled a 3D network under moderate heating conditions. The composition of the aerogel was precisely controlled by adjusting the initial concentration of the MOF suspension. The minimum reflection losses of -58.1 dB and -46.2 dB and the effective bandwidths of 6.48 GHz and 7.92 GHz were achieved respectively; Reference 2 "Yu, W., B. Liu and X. Zhao. Ultralight MOF-Derived Ni3S2@N, S-Co doped Graphene Aerogels for High-Performance Microwave Absorption. Nanomaterials 12(2022)." reported the preparation of a high-performance Ni3S2@N, S co-doped graphene aerogel by gelation using Ni-MOF nanorods as the precursor. The three-dimensional structure and porous structure promoted conductivity, magnetic loss, and multiple scattering reflections. When the thickness was 2.0 mm, the minimum reflection absorption reached -46.9 dB, and when the thickness was 2.3 mm, the effective bandwidth was 6.3 GHz.

[0007] The above-mentioned references all prepared composites of MOF and graphene, and when the minimum reflection loss was achieved, a relatively wide effective bandwidth was also obtained. In order to achieve thin, light, and wide microwave absorption performance in the effective frequency range of 2-18 GHz, the present invention provides a CAU-10-H carbon-based derivative / rGO composite microwave absorption material and its preparation method, enabling the effective combination and application of multiple mechanisms to obtain good microwave absorption performance. Summary of the Invention

[0008] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a CAU-10-H MOF carbon-based derivative and reduced graphene oxide composite microwave absorption material, its preparation method and application.

[0009] To achieve the above object, the present invention provides the following technical solutions: A preparation method of an Al-MOF-derived CAU-Al / rGO composite microwave absorption material, comprising the following steps: (1) Prepare reduced graphene oxide. Weigh graphite oxide powder and ascorbic acid reducing agent according to the mass ratio, add deionized water and stir, and then use cell disruption to obtain an aqueous solution of reduced graphene oxide. Then, through hydrothermal method and vacuum freeze-drying method, black reduced graphene oxide black powder is obtained. (2) Prepare CAU-10-H carbon-based derivative. Put the white powder CAU-10-H(Al) precursor into the quartz tube in the tube furnace, seal the quartz tube, slowly introduce argon gas inside the quartz tube, and fill the tube with gas. Then, heat up to 200°C and 300°C respectively until the temperature is constant, and carbonize under argon atmosphere to form CAU-Al(200) and CAU-Al(300) respectively. (3) Preparation of the composite material: Mix the CAU-Al(200) and CAU-Al(300) obtained in step (2) with the reduced graphene oxide powder obtained in step (1) according to the mass ratio, and uniformly stir to obtain the CAU-Al(200, 300) / rGO composite microwave absorption material.

[0010] Further, in step (1), dissolve the graphite oxide powder and ascorbic acid reducing agent in deionized water, stir to obtain a brown-yellow solution, and the time of cell disruption is 30 minutes.

[0011] Further, in step (1), the aqueous solution of graphene oxide is heated in a water bath at a temperature of 95°C for 0.5 - 1 hour by the hydrothermal method; in the vacuum freeze-drying method, freeze-dry for 48 hours, and the freezing temperature is -30~-50°C.

[0012] Further, in step (2), when heat-treating under argon atmosphere, the heating rate is 1 - 5°C / min, and carbonize for half an hour.

[0013] Further, in step (3), mix CAU-Al(200) and CAU-Al(300) with the reduced graphene oxide powder in three different mass ratios of 1:1, 1:2 or 1:3 to form the CAU-Al(200, 300) / rGO composite microwave absorption material.

[0014] Further, in step (2), a white powder CAU-10-H(Al) precursor was prepared by solvothermal method using aluminum sulfate octadecahydrate, isophthalic acid and DMF.

[0015] Further, in step (1), graphite oxide powder was prepared. The flake graphite used had a mesh size of 300. 1 g of flake graphite was mixed with 0.5 g of NaNO3 and 48 ml of H2SO4 in an ice bath. 6 g of KMnO4 was added in batches, and the ice bath time was 2 h. The temperature was raised to 35 °C and stirred for 4 h. 45 ml of deionized water was added, and the temperature was raised to 90 °C and heated for 30 min. After cooling, 60 ml of deionized water and 6 ml of H2O2 were added. It was washed three times with dilute hydrochloric acid with a concentration of 5%, and then washed with deionized water until neutral.

[0016] Further, the temperature in the solvothermal method was 135 °C and the heat preservation time was 12 hours.

[0017] An Al-MOF-derived CAU-Al(200, 300) / rGO composite microwave absorbing material was prepared by the above preparation method.

[0018] By adopting the above technical solution, the beneficial effects of the present invention are as follows: Compared with the existing technology, in the present invention, MOF as an electromagnetic microwave absorbing material has the advantages of adjustable structure and wide effective frequency band. Among them, the CAU structure type of MOF has less research on electromagnetic wave absorption. Al-based MOF has attracted extensive attention because of its low price, low toxicity, high chemical stability and high thermal stability.

[0019] The molecular structure of CAU-10-H is composed of cis-connected AlO6 polyhedra and isophthalic acid, showing good stability at a temperature of 430 °C and also having good stability in aqueous solution. Aerogel, as a new material with a three-dimensional porous structure, has the characteristics of low density, high porosity, light weight and wide effective frequency band in microwave absorbing materials. Although MOF has low conductivity, graphene, which has been reported a lot in recent years, has the advantages of light weight, large specific surface area, etc., and its conductivity is relatively stable. However, graphene with a higher conductivity still has the disadvantages of poor impedance matching and poor attenuation loss as a microwave absorbing material. Therefore, graphene is combined with other dielectric loss materials or magnetic loss materials to increase interfacial polarization, reduce material loss and improve microwave absorbing performance.

[0020] The present invention prepares a MOF-based / reduced graphene oxide composite material through simple and rapid methods such as solvothermal method, water bath heating method, heat treatment, freeze drying, etc. Compared with the pure MOF wave-absorbing material, doping MOF particles in reduced graphene oxide improves the dielectric loss ability of the material itself and provides interfacial polarization relaxation loss. The high content, controllable structure, and uniform distribution of MOF form a composite material in combination with reduced graphene oxide, which is not only light in weight but also improves the impedance matching with air and enhances the wave-absorbing performance of the material in electromagnetic wave applications. Description of the Drawings

[0021] Figure 1 XRD schematic diagrams of CAU-10-H, carbon-based derivatives of CAU-10-H, rGO, and CAU-10-H carbon-based derivative / rGO composite materials of the present invention at different annealing temperatures and mass ratios; Figure 2 SEM images of CAU-10-H carbon-based derivative / rGO composite materials of the present invention at different mass ratios at 200°C and 300°C; Figure 3a Reflection loss diagram of the CAU-10-H carbon-based derivative / rGO composite material of Example 1 at 200°C with a mass ratio of CAU-10-H carbon-based derivative to rGO of 1:1; Figure 3b Reflection loss diagram of the CAU-10-H carbon-based derivative / rGO composite material of Example 2 at 200°C with a mass ratio of CAU-10-H carbon-based derivative to rGO of 1:2; Figure 3c Reflection loss diagram of the CAU-10-H carbon-based derivative / rGO composite material of Example 3 at 200°C with a mass ratio of CAU-10-H carbon-based derivative to rGO of 1:3; Figure 3d Reflection loss diagram of the CAU-10-H carbon-based derivative / rGO composite material of Example 4 at 300°C with a mass ratio of CAU-10-H carbon-based derivative to rGO of 1:1; Figure 3e Reflection loss diagram of the CAU-10-H carbon-based derivative / rGO composite material of Example 5 at 300°C with a mass ratio of CAU-10-H carbon-based derivative to rGO of 1:2; Figure 3f Reflection loss diagram of the CAU-10-H carbon-based derivative / rGO composite material of Example 6 at 300°C with a mass ratio of CAU-10-H carbon-based derivative to rGO of 1:3. Detailed Embodiments

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0023] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0024] The present invention relates to a preparation method of a composite absorbing material of CAU-10-H MOF carbon-based derivative and reduced graphene oxide. Using CAU-10-H MOF as the matrix and doping reduced graphene oxide, it includes the following steps: (1) Perform a solvothermal reaction on aluminum sulfate octadecahydrate, isophthalic acid, and DMF to prepare the precursor MOF CAU-10-H. The temperature in the solvothermal method used for preparing the precursor CAU-10-H is 135 °C, and the heat preservation time is 12 hours.

[0025] (2) Heat CAU-10-H in a tube furnace to 200 °C and 300 °C to form a CAU-10-H carbon-based derivative. The heating rate of the tube furnace is 1 - 5 °C / min, the temperature of the tube furnace is 200 °C and 300 °C, and the heat treatment time is 30 minutes.

[0026] (3) Prepare an aqueous solution of graphene oxide. Mix graphite oxide powder, ascorbic acid, and deionized water, and perform cell disruption for 30 minutes to form an aqueous solution of graphene oxide. The flake graphite used for preparing graphite oxide is 300 mesh. Mix 1 g of graphite with 0.5 g of NaNO3 and 48 ml of H2SO4, and perform ice bath. Add 6 g of KMnO4 in batches, and the ice bath time is 2 h. Raise the temperature to 35 °C and stir for 4 hours. Add 45 ml of deionized water, raise the temperature to 90 °C, and heat for 30 min. After cooling, add 60 ml of deionized water and 6 ml of H2O2, wash three times with 5% dilute hydrochloric acid, and then wash with deionized water until neutral.

[0027] (4) Put the graphene oxide aqueous solution into a water bath and heat it in the water bath to reduce it to reduced graphene oxide. Vacuum freeze-dry the reduced graphene oxide for 48 hours to form a black powder of reduced graphene oxide. Heat the prepared reduced graphene oxide aqueous solution in a water bath for 1 hour at a temperature of 95 °C. Pre-vacuum freeze-dry it at a freezing temperature of -30 to -50 °C for 48 hours.

[0028] (5) Mix CAU-Al(200), CAU-Al(300) with the reduced graphene oxide powder at three different mass ratios of 1:1, 1:2, and 1:3 respectively to form the CAU-Al(200, 300) / rGO composite microwave absorbing material. The total mass of CAU-10-H and the reduced graphene oxide powder is 40 mg.

[0029] Example 1:

[0030] This example provides a CAU-10-H carbon-based derivative / reduced graphene oxide composite material, and its preparation method is specifically as follows: (1) Prepare the precursor CAU-10-H MOF. Ultrasonically dissolve aluminum sulfate octadecahydrate, isophthalic acid, N,N-dimethylformamide (DMF) and deionized water for two hours. Put the mixed solution into a NOVA microwave synthesizer for heating at a temperature of 135 °C and a holding time of 12 hours. After cooling to room temperature, wash it three times with N,N-dimethylformamide (DMF), then put it into deionized water and ultrasonically treat it for two hours, centrifuge and filter, and dry it to obtain a white powder.

[0031] (2) Put the precursor CAU-10-H MOF into the porcelain boat of a tube furnace. The heating rate of the tube furnace is 1 - 5 °C / min, and anneal it under an argon atmosphere. The annealing temperature of the tube furnace is 200 °C and 300 °C, and the heat treatment time is 30 minutes; obtain the annealed CAU-10-H carbon-based derivatives, denoted as CAU-Al(200) and CAU-Al(300) respectively.

[0032] (3) Prepare the reduced graphene oxide powder. Put graphite oxide powder and ascorbic acid into deionized water, and crush it with an ultrasonic cell crusher for 30 minutes. Then put the graphene oxide aqueous solution into a water bath and heat it at a temperature of 95 °C for 40 minutes to obtain a reduced graphene oxide aqueous solution. Put the reduced graphene oxide aqueous solution into a vacuum freeze dryer for freezing to obtain the reduced graphene oxide powder.

[0033] (4) The mass ratio of CAU-Al(200) to the reduced graphene oxide powder is 1:1.

[0034] Example 2:

[0035] This embodiment provides a CAU-10-H carbon-based derivative / reduced graphene oxide composite material, and its preparation method specifically comprises the following steps: (1) Prepare the precursor CAU-10-H MOF. Ultrasonically dissolve aluminum sulfate octadecahydrate, isophthalic acid, N,N-dimethylformamide (DMF) and deionized water for two hours. Put the mixed solution into a NOVA microwave synthesizer for heating at a temperature of 135 °C for 12 hours. After cooling to room temperature, wash it three times with N,N-dimethylformamide (DMF), then put it into deionized water for ultrasonic treatment for two hours, centrifuge and filter, and dry it to obtain a white powder.

[0036] (2) Put the precursor CAU-10-H MOF into a porcelain boat in a tube furnace. The heating rate of the tube furnace is 1-5 °C / min. Anneal it under an argon atmosphere. The annealing temperature of the tube furnace is 200 °C and 300 °C, and the heat treatment time is 30 minutes. Obtain the annealed CAU-10-H carbon-based derivatives, denoted as CAU-Al(200) and CAU-Al(300) respectively.

[0037] (3) Prepare reduced graphene oxide powder. Put graphite oxide and ascorbic acid into deionized water and crush it with a cell crusher for 30 minutes. Put the graphene oxide aqueous solution into a water bath at a heating temperature of 95 °C for 40 minutes to obtain a reduced graphene oxide aqueous solution. Freeze the reduced graphene oxide aqueous solution in a vacuum freeze dryer to obtain reduced graphene oxide powder.

[0038] (4) The mass ratio of CAU-Al(200) to reduced graphene oxide powder is 1:2.

[0039] Example 3:

[0040] This embodiment provides a CAU-10-H carbon-based derivative / reduced graphene oxide composite material, and its preparation method specifically comprises the following steps: (1) Prepare the precursor CAU-10-H MOF. Ultrasonically dissolve aluminum sulfate octadecahydrate, isophthalic acid, N,N-dimethylformamide (DMF) and deionized water for two hours. Put the mixed solution into a NOVA microwave synthesizer for heating at a temperature of 135 °C for 12 hours. After cooling to room temperature, wash it three times with N,N-dimethylformamide (DMF), then put it into deionized water for ultrasonic treatment for two hours, centrifuge and filter, and dry it to obtain a white powder.

[0041] (2) Place the precursor CAU-10-H MOF in a porcelain boat in a tube furnace. The heating rate of the tube furnace is 1-5 °C / min, and anneal it under an argon atmosphere. The annealing temperature of the tube furnace is 200 °C and 300 °C, and the heat treatment time is 30 minutes. The annealed CAU-10-H carbon-based derivatives are obtained, denoted as CAU-Al(200) and CAU-Al(300) respectively.

[0042] (3) Prepare reduced graphene oxide powder. Put graphite oxide and ascorbic acid into deionized water, and crush it with a cell crusher for 30 minutes. Place the graphene oxide aqueous solution in a water bath, heat it at 95 °C for 40 minutes to obtain a reduced graphene oxide aqueous solution. Freeze the reduced graphene oxide aqueous solution in a vacuum freeze dryer to obtain reduced graphene oxide powder.

[0043] (4) The mass ratio of CAU-Al(200) to reduced graphene oxide powder is 1:3.

[0044] Example 4:

[0045] This example provides a CAU-10-H carbon-based derivative / reduced graphene oxide composite material, and its preparation method is specifically as follows: (1) Prepare the precursor CAU-10-H MOF. Ultrasonically dissolve aluminum sulfate octadecahydrate, isophthalic acid, N,N-dimethylformamide (DMF) and deionized water for two hours. Place the mixed solution in a NOVA microwave synthesizer for heating at 135 °C for 12 hours. After cooling to room temperature, wash it three times with N,N-dimethylformamide (DMF), then ultrasonically treat it in deionized water for two hours, centrifuge and filter, and dry it to obtain a white powder.

[0046] (2) Place the precursor CAU-10-H MOF in a porcelain boat in a tube furnace. The heating rate of the tube furnace is 1-5 °C / min, and anneal it under an argon atmosphere. The annealing temperature of the tube furnace is 200 °C and 300 °C, and the heat treatment time is 30 minutes. The annealed CAU-10-H carbon-based derivatives are obtained, denoted as CAU-Al(200) and CAU-Al(300) respectively.

[0047] (3) Prepare reduced graphene oxide powder. Put graphite oxide and ascorbic acid into deionized water, and crush it with a cell crusher for 30 minutes. Place the graphene oxide aqueous solution in a water bath, heat it at 95 °C for 40 minutes to obtain a reduced graphene oxide aqueous solution. Freeze the reduced graphene oxide aqueous solution in a vacuum freeze dryer to obtain reduced graphene oxide powder.

[0048] (4) The mass ratio of CAU-Al(300) to reduced graphene oxide powder is 1:1.

[0049] Example 5:

[0050] This example provides a CAU-10-H carbon-based derivative / reduced graphene oxide composite material, and its preparation method is specifically as follows: (1) Prepare the precursor CAU-10-H MOF. Ultrasonically dissolve aluminum sulfate octadecahydrate, isophthalic acid, N,N-dimethylformamide (DMF), and deionized water for two hours. Put the mixed solution into a NOVA microwave synthesizer for heating at a temperature of 135 °C and a holding time of 12 hours. After cooling to room temperature, wash it three times with N,N-dimethylformamide (DMF), then put it into deionized water and ultrasonically treat for two hours, centrifuge and filter, and dry to obtain a white powder.

[0051] (2) Put the precursor CAU-10-H MOF into the porcelain boat of a tube furnace. The heating rate of the tube furnace is 1-5 °C / min, and anneal it under an argon atmosphere. The annealing temperature of the tube furnace is 200 °C and 300 °C, and the heat treatment time is 30 minutes. Obtain the annealed CAU-10-H carbon-based derivatives, denoted as CAU-Al(200) and CAU-Al(300) respectively.

[0052] (3) Prepare reduced graphene oxide powder. Put graphite oxide and ascorbic acid into deionized water and crush it with a cell crusher for 30 minutes. Put the graphene oxide aqueous solution into a water bath and heat it at a temperature of 95 °C for 40 minutes to obtain a reduced graphene oxide aqueous solution. Freeze the reduced graphene oxide aqueous solution in a vacuum freeze dryer to obtain reduced graphene oxide powder.

[0053] (4) The mass ratio of CAU-Al(300) to reduced graphene oxide powder is 1:2.

[0054] Example 6:

[0055] This example provides a CAU-10-H carbon-based derivative / reduced graphene oxide composite material, and its preparation method is specifically as follows: (1) Prepare the precursor CAU-10-H MOF. Ultrasonically dissolve aluminum sulfate octadecahydrate, isophthalic acid, N,N-dimethylformamide (DMF), and deionized water for two hours. Put the mixed solution into a NOVA microwave synthesizer for heating at a temperature of 135 °C and a holding time of 12 hours. After cooling to room temperature, wash it three times with N,N-dimethylformamide (DMF), then put it into deionized water and ultrasonically treat for two hours, centrifuge and filter, and dry to obtain a white powder.

[0056] (2) Place the precursor CAU-10-H MOF in a porcelain boat in a tube furnace. The heating rate of the tube furnace is 1 - 5 °C / min. Anneal it under an argon atmosphere. The annealing temperature of the tube furnace is 200 °C and 300 °C, and the heat treatment time is 30 minutes. Obtain the annealed CAU-10-H carbon-based derivatives, denoted as CAU-Al(200) and CAU-Al(300) respectively.

[0057] (3) Prepare reduced graphene oxide powder. Put graphite oxide and ascorbic acid into deionized water and crush it with a cell crusher for 30 minutes. Place the graphene oxide aqueous solution in a water bath pot, heat it at a temperature of 95 °C for 40 minutes to obtain a reduced graphene oxide aqueous solution. Freeze the reduced graphene oxide aqueous solution in a vacuum freeze dryer to obtain reduced graphene oxide powder.

[0058] (4) The mass ratio of CAU-Al(300) to reduced graphene oxide powder is 1:3.

[0059] Characterize reduced graphene oxide, CAU-Al(200, 300), and CAU-Al(200, 300) / reduced graphene oxide composites. The results are as follows: Figure 1 is the XRD pattern of reduced graphene oxide, CAU-Al(200, 300), and CAU-Al(200, 300) / reduced graphene oxide composites. By comparing with the standard pdf card, it is proved that reduced graphene oxide and CAU-Al(200, 300) are successfully prepared. From the peaks, it shows that both CAU-Al(200, 300) and reduced graphene oxide are present in the CAU-Al(200, 300) / reduced graphene oxide composites; Figure 2 is the SEM image of the CAU-Al(200, 300) / reduced graphene oxide composite at 200 °C and 300 °C. It can be seen from the SEM image that there are wrinkled graphene nanosheets in the composite, and the particles after annealing of CAU-10-H are attached to the graphene nanosheets.

[0060] Figures 3a - 3f is the phase diagram of the reflection loss of the CAU-Al(200, 300) / reduced graphene oxide composite varying with the microwave frequency and the thickness of the microwave absorbing material.

[0061] Figure 3aThe phase diagram of the reflection loss of the CAU-Al(200) / reduced graphene oxide composite material at 200 °C with a mass ratio of CAU-Al(200) to reduced graphene oxide of 1:1 as a function of microwave frequency and the thickness of the microwave absorbing material. When the thickness is 2 mm, its minimum reflection loss value is -23.31 dB, and the effective bandwidth reaches 5.83 GHz.

[0062] Figure 3b The phase diagram of the reflection loss of the CAU-Al(200) / reduced graphene oxide composite material at 200 °C with a mass ratio of CAU-Al(200) to reduced graphene oxide of 1:2 as a function of microwave frequency and the thickness of the microwave absorbing material. When the thickness is 2 mm, the effective bandwidth reaches 9.06 GHz.

[0063] Figure 3c The phase diagram of the reflection loss of the CAU-Al(200) / reduced graphene oxide composite material at 200 °C with a mass ratio of CAU-Al(200) to reduced graphene oxide of 1:3 as a function of microwave frequency and the thickness of the microwave absorbing material. When the thickness is 2 mm, the effective bandwidth reaches 3.87 GHz.

[0064] Figure 3d The phase diagram of the reflection loss of the CAU-Al(300) / reduced graphene oxide composite material at 300 °C with a mass ratio of CAU-Al(300) to reduced graphene oxide of 1:1 as a function of microwave frequency and the thickness of the microwave absorbing material. When the thickness is 2.5 mm, its minimum reflection loss value is -44.81 dB, and the effective bandwidth reaches 5.44 GHz.

[0065] Figure 3e The phase diagram of the reflection loss of the CAU-Al(300) / reduced graphene oxide composite material at 300 °C with a mass ratio of CAU-Al(300) to reduced graphene oxide of 1:2 as a function of microwave frequency and the thickness of the microwave absorbing material.

[0066] Figure 3f The phase diagram of the reflection loss of the CAU-Al(300) / reduced graphene oxide composite material at 300 °C with a mass ratio of CAU-Al(300) to reduced graphene oxide of 1:3 as a function of microwave frequency and the thickness of the microwave absorbing material.

[0067] The composite materials prepared in the examples of the present invention were subjected to microwave absorption experiments: The six groups of samples obtained in the examples were pressed into a circular ring with paraffin at a mass ratio of 1:3. The inner diameter of the ring was 3 mm, the outer diameter was 7 mm, and the thickness was 1 - 1.5 mm. A vector network analyzer was used to measure the real part and imaginary part of the dielectric constant, and the real part and imaginary part of the magnetic permeability of the material. Finally, the microwave absorption performance of the material was calculated based on the electromagnetic parameters.

[0068] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any ordinary changes and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing an Al-MOF-derived CAU-Al / rGO composite absorbing material, characterized in that: The following steps are involved: (1) preparing reduced graphene oxide, weighing graphite oxide powder and ascorbic acid reducing agent according to a mass ratio, adding deionized water for stirring, crushing the cells to obtain a reduced graphene oxide aqueous solution, and then obtaining black reduced graphene oxide black powder by a hydrothermal method and a vacuum freeze drying method; (2) Preparation of CAU-10-H carbon-based derivatives: placing a white powder CAU-10-H (Al) precursor into a quartz tube in a tube furnace, sealing the quartz tube, slowly introducing argon gas into the quartz tube, and filling the tube with gas; then heating to 200°C and 300°C respectively until the temperature is constant, and carbonizing in an argon atmosphere to form CAU-Al (200) and CAU-Al (300) respectively; (3) Preparation of composite materials: CAU-Al (200) and CAU-Al (300) obtained in step (2) are mixed with the reduced graphene oxide powder obtained in step (1) in a certain mass ratio, and the mixture is stirred evenly to obtain a CAU-Al (200, 300) / rGO composite absorber.

2. The method for preparing an Al-MOF-derived CAU-Al / rGO composite absorbing material according to claim 1, characterized in that: In step (1), graphite oxide powder and ascorbic acid reducing agent are dissolved in deionized water, and a brown-yellow solution is obtained after stirring. The cell crushing time is 30 minutes.

3. The method for preparing an Al-MOF-derived CAU-Al / rGO composite absorbing material according to claim 1, characterized in that: In step (1), the graphene oxide aqueous solution is heated in a water bath at a temperature of 95° C. for 0.5-1 hour by a hydrothermal method; and freeze-dried for 48 hours by a vacuum freeze-drying method at a freezing temperature of -30 to -50° C.

4. The method for preparing an Al-MOF-derived CAU-Al / rGO composite absorbing material according to claim 1, characterized in that: In step (2), during the heat treatment in an argon atmosphere, the heating rate is 1-5°C / min and the carbonization time is half an hour.

5. The method for preparing an Al-MOF-derived CAU-Al / rGO composite absorbing material according to claim 1, characterized in that: In step (3), CAU-Al (200), CAU-Al (300) and reduced graphene oxide powder are mixed in three different mass ratios of 1:1, 1:2 or 1:3 to form a CAU-Al (200, 300) / rGO composite absorber.

6. The method for preparing an Al-MOF-derived CAU-Al / rGO composite absorbing material according to claim 1, characterized in that: In step (2), aluminum sulfate 18hydrate, isophthalic acid and DMF are subjected to a solvothermal method to prepare a white powder CAU-10-H(Al) precursor.

7. The method for preparing an Al-MOF derived CAU-Al / rGO composite absorbing material according to claim 1, characterized in that: In step (1), graphite oxide powder is prepared. The flake graphite used is 300 mesh. 1 g of flake graphite is mixed with 0.5 g of NaNO3 and 48 ml of H2SO4 in an ice bath. Add 6 g KMnO4 in batches, ice bath for 2 h, raise the temperature to 35 °C and stir for 4 hours; Add 45 ml of deionized water, raise the temperature to 90°C, heat the reaction for 30 min, add 60 ml of deionized water and 6 ml of H2O2 after cooling, wash three times with 5% dilute hydrochloric acid, and then wash with deionized water until neutral.

8. The method for preparing an Al-MOF-derived CAU-Al / rGO composite absorbing material according to claim 6, characterized in that: The temperature in the solvothermal method was 135° C. and the holding time was 12 hours.

9. An Al-MOF derived CAU-Al (200, 300) / rGO composite absorbing material, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 8.

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