CN105255446A - Reduced graphene oxide and nano cerium oxide composite microwave absorbing material and preparation method thereof - Google Patents

Abstract

The present invention specifically relates to a microwave-absorbing material and a preparation method of reducing graphene oxide and nano-cerium oxide composite. The graphene oxide is prepared by the improved Hummers method, and the graphene oxide aqueous solution is mixed with cerium nitrate at a mass ratio of 1:25, and at the same time The pH is adjusted to 10, and a one-step hydrothermal method is used to reduce graphene oxide while generating nano-cerium oxide, so as to obtain a microwave absorbing material composited by reduced graphene oxide and nano-cerium oxide. The microwave absorption parameters of composite materials are tested by vector network analyzer, and the microwave reflection loss of composite materials is calculated by classical coaxial line theory. The results show that the reduced graphene oxide/nano-cerium oxide composite microwave absorbing material has excellent microwave absorption performance, high absorption strength, and wide absorption frequency band. Compared with nano-cerium oxide, the microwave absorption performance is greatly improved. Therefore, the present invention has broad application prospects, and has extremely important significance for expanding the industrial application of rare earth oxides and national defense construction.

Description

A microwave absorbing material composited with reduced graphene oxide and nano-cerium oxide and its preparation method

technical field

The invention belongs to the technical field of functional materials, and in particular relates to a microwave absorbing material and a preparation method.

Background technique

With the development of military stealth technology and civilian anti-electromagnetic interference technology, microwave absorbing materials (referred to as absorbing materials) have become a research hotspot, and this type of material has gradually become an important branch of applied functional materials. Absorbing materials refer to a class of materials that can absorb and attenuate incident electromagnetic waves, convert their electromagnetic energy into heat or other forms of energy and dissipate them, or make electromagnetic waves disappear due to interference.

The main disadvantages of traditional absorbing materials, such as ferrite, graphite, and ceramics, are high density, narrow absorption frequency band, and insufficient absorption strength, so they cannot meet the requirements of "thin, light, wide, and strong" absorbing materials. In recent years, the application of nanocomposite materials in microwave absorption has become a research hotspot. The unique quantum size effect, macroscopic quantum tunneling effect and interface effect of nanomaterials have changed the physical properties of materials such as electricity and magnetism. At the same time of performance, it has the characteristics of broadband, good compatibility, light weight, and thin thickness. It is a very promising stealth material.

Carbon-based materials have been widely used in the fields of electromagnetic shielding and wave-absorbing materials. As a representative of new carbon materials, graphene has been a hot spot in the field of functional materials for its unique mechanical, electrical, optical and magnetic properties since its appearance. The special two-dimensional flake single-layer carbon atom honeycomb structure of graphene endows it with advantages such as high specific surface area, high electron mobility and high mechanical strength. Compared with traditional materials, graphene composite materials can more easily meet the characteristics of impedance matching and meet the requirements of "thin, light, wide and strong" absorbing materials.

Cerium oxide (CeO ₂ ) is the most widely used rare earth metal oxide in industry. Its molecular formula is CeO ₂ and its molecular weight is 172.12. It exists in nature as a fluorite structure. CeO2 nanomaterials have important industrial applications in light _- emitting devices, automobile exhaust purification catalysis, solid oxide fuel cell electrolytes, and novel anti-ultraviolet absorption.

In the CeO ₂ crystal, due to the existence of oxygen defects, Ce ions usually have an intermediate valence state, that is, Ce ⁴⁺ and Ce ³⁺ . Under certain conditions, Ce ⁴⁺ and Ce ³⁺ are easily converted to each other, so that CeO ₂ , a large number of oxygen vacancies are formed inside, therefore, fluorite-type CeO ₂ has a strong ability to store and release oxygen. Many industrial applications of cerium oxide have been benefited from its special oxygen vacancy effect.

A large number of oxygen vacancy defects inside the crystal, accompanied by a high concentration of +3 valent cerium ions, will improve the electrical conductivity of CeO ₂ , which will cause conduction loss under the influence of external electromagnetic waves and attenuate electromagnetic waves; at the same time, the formation of oxygen vacancies in the crystal lattice The generation of a large number of free electrons will intensify the charge polarization and enhance its microwave absorption performance.

The preparation of graphene _- based cerium _oxide nanocomposites can improve the microwave absorption performance of CeO2 nanocomposites by making use of the excellent carrier function of graphene and the special oxygen vacancy effect of CeO2.

Contents of the invention

In order to expand the application of rare earth oxide nanomaterials in the field of microwave absorption, the present invention provides a microwave absorption material composited with reduced graphene oxide (RGO) and nano cerium oxide (CeO ₂ ) and a preparation method.

A microwave-absorbing material composited by reduced graphene oxide and nano-cerium oxide prepares graphite oxide by the improved Hummers method, mixes the graphene oxide solution with cerium nitrate hexahydrate at a mass ratio of 1:25, adjusts the pH value to 10, and adopts one-step Hydrothermal method, reducing graphene oxide while generating nano-cerium oxide, and preparing a composite microwave absorbing material of reduced graphene oxide and nano-cerium oxide;

The characteristics of the composite microwave absorbing material are: the surface of the reduced graphite oxide flakes is evenly loaded with nano-cerium oxide particles, and the adjacent flakes are separated from each other, forming a layered sandwich structure, which contributes to the improvement of microwave absorption performance ;

The average nanoparticle size of the nano-cerium oxide (CeO ₂ ) is 15 nm, which has a prominent quantum size effect and an excellent oxygen vacancy effect;

The weight ratio of reduced graphene oxide (RGO) and nano cerium oxide (CeO ₂ ) in the composite microwave absorbing material is 1:10;

When the composite microwave absorbing material is a coating with a thickness of 1.5 to 2.0mm, the reflection loss at the frequency of 4.3 to 17 GHz is -32 to -10dB; the electromagnetic wave absorption is over 90%.

The specific steps for preparing the composite microwave absorbing material of reduced graphene oxide and nano-cerium oxide are as follows:

(1) Preparation of graphite oxide

Graphite oxide was prepared by the improved Hummers method, 3g of graphite powder and 2g of sodium nitrate (NaNO ₃ ) were added to a 250mL beaker, and 70mL of concentrated sulfuric acid with a concentration of 95-98% was slowly added along the wall of the beaker and stirred evenly; Under bath conditions, add 10 g of potassium permanganate (KMnO ₄ ) in 5 times, 2 g each time, and stir for one hour; stir in a 35˚C water bath for 2 h to obtain a mixed solution; add 140 mL of deionized water Slowly added to the mixed solution and stirred for 15 min. At this time, the temperature of the system was raised to 88-92 °C, and hydrogen peroxide (H ₂ O ₂ ) with a concentration of 30% was added dropwise until the reaction solution turned bright yellow; Filtrate hot and wash with 1:10 dilute hydrochloric acid solution to remove excess metal ions; centrifuge at high speed and wash repeatedly until the pH value is 7; freeze-dry for 48 hours to obtain graphite oxide;

(2) Preparation of microwave absorbing materials composited by reduced graphene oxide and nano-cerium oxide

Dissolve 20 mg of graphite oxide in 60 mL of deionized water and ultrasonically disperse for 1 h to obtain 60 mL of brown-yellow graphene oxide solution; take 0.5 g of cerium nitrate hexahydrate (Ce(NO ₃ ) ₃ 6H ₂ O) into In 60mL of graphene oxide solution, stir magnetically; until cerium nitrate hexahydrate is completely dissolved, slowly add 3 mL of ammonia solution with a concentration of 25-28% to the reaction solution under the action of ultrasound, and the pH of the reaction solution is now 9 ~11; transfer the reaction solution to a hydrothermal reaction kettle, and conduct a hydrothermal reaction at 180 ^° C for 24 hours; centrifuge, wash with water, and wash and purify with ethanol; vacuum-dry at 60°C for 24 hours to obtain reduced graphene oxide and nano-cerium oxide (RGO/CeO ₂ ) composite microwave absorbing material.

The microwave absorbing material composited by reduced graphene oxide and nano cerium oxide of the present invention can be used as an excellent microwave absorbing agent, and its microwave absorbing performance parameters are obtained by the following detection means:

Mix the microwave absorbing material composed of reduced graphene oxide and nano-cerium oxide with paraffin (the volume fraction of the composite microwave absorbing material accounts for 30%), keep warm at 80˚C for half an hour to melt the paraffin, stir evenly, put it into a mold, and A coaxial ring with an inner diameter of 3.04 mm and an outer diameter of 7.00 mm was made under a pressure of 2 Mpa, and its thickness was ground to 2 mm. The imaginary part is to calculate the reflection loss of the microwave absorbing material of the present invention through the classical coaxial line theory.

The microwave absorption performance of the microwave absorbing material composed of RGO and nano-CeO ₂ was tested by the AV3629D (the 41st Research Institute of China Electronics Group) vector network analyzer, using the APC7 coaxial fixture with a length of 99.898 mm, and the calibration part was AV31101. The test frequency range is 2-18 GHz, and the test sample is a coaxial ring with a thickness of 2 mm composed of a composite microwave absorbing material and paraffin wax. Through fitting, the microwave absorbing material of the present invention is obtained within the range of 1-5 mm in thickness. reflection loss.

The crystal phase structure of the microwave absorbing material composited with RGO and nano _- CeO2 was confirmed by X-ray diffraction (XRD) (see Fig. 1). The XRD results show that the composite material has a typical cubic fluorite structure, and its crystal phase is consistent with that of CeO ₂ . The (111) crystal plane is calculated using the Debye-Scherrer formula, and the nanocrystalline grain size is 15 nm. There is no characteristic peak of graphene oxide in the XRD pattern of the material, indicating that after hydrothermal treatment, graphene oxide is effectively reduced to form reduced graphene oxide (RGO).

The microstructure of the microwave-absorbing material composited with RGO and nano-CeO2 was observed by transmission electron microscopy (TEM) (see Figure ₂ ). The CeO ₂ nanoparticles are uniformly dispersed on the monolithic reduced graphene oxide, showing a hexagonal morphology. Particle measurement results show that the average size of CeO2 nanoparticles is ₁₅ nm, which is consistent with the XRD results.

The microwave-absorbing material composited by RGO and nano _- CeO2 has high-efficiency microwave-absorbing properties (see Figure 3). When the sample coating thickness ( d ) is 1.5 mm, the best reflection loss is -32 dB at a frequency of 17 GHz. When the coating thickness is 2.0 mm, the frequency bandwidth with reflection loss lower than -10 dB (electromagnetic wave absorption is more than 90%) is 4.3 GHz. Compared with nano-cerium oxide, this composite material has high microwave absorption strength and wide absorption band (see Figure 4).

The microwave absorbing material composited by RGO and nano-CeO ₂ uses graphene oxide as the precursor, mainly because the surface of graphene oxide has a large number of oxygen-containing functional groups, such as hydroxyl, carboxyl, epoxy, etc., these functional groups can be regarded as reactive Point, when cerium ions are added, the electrostatic attraction will make the cerium ions adsorb on the graphene oxide sheet, which is conducive to the uniform nucleation of crystals. Graphene oxide will be reduced during the hydrothermal process, and most of the oxygen-containing functional groups will disappear. At this time, there will be van der Waals force between the reduced graphene oxide and CeO ₂ , so that CeO ₂ is tightly immobilized on the reduced graphene oxide sheet.

In the preparation process of the microwave absorbing material composited by RGO and nano _- CeO2, the precipitant ammonia water was added dropwise, supplemented by ultrasonic action, in order to improve the dispersion of CeO2 nanoparticles on the graphene _oxide sheet. In the initial stage of crystal nucleation, ultrasonic action can improve the crystal growth environment and increase the dispersion of crystal nuclei, so that the nanoparticles can be uniformly dispersed, which also helps to improve the microwave absorption performance of the material.

Beneficial technical effect of the present invention is embodied in the following aspects:

1. The microwave absorbing material composited by reduced graphene oxide and nano-cerium oxide of the present invention fully utilizes the characteristics of high electron mobility and large specific surface area of graphene, and simultaneously takes into account the remarkable oxygen vacancy effect of nano-cerium oxide, thereby obtaining the absorption Cerium oxide nano-composite material with excellent wave performance. Compared with nano-cerium oxide, this composite microwave absorbing material has the advantages of strong microwave absorption and wide absorption frequency band. The best microwave reflection loss is -32dB. When the coating thickness is 2.0mm When the reflection loss is lower than -10dB (the electromagnetic wave absorption is more than 90%), the frequency bandwidth is 4.3GHz.

2. During the preparation of hydrothermal precursors, the ultrasonic field is used to assist, and the nucleation environment of nanocrystals is effectively improved through ultrasonic radiation, which improves the dispersion of nanoparticles on the graphene carrier and prevents the formation of graphene sheets. of stacks.

3. The preparation process of the present invention is simple, low in cost and good in safety, without adding reducing agent and surfactant during the synthesis process, and is environmentally friendly. The invention has broad development and application prospects, and has extremely important significance for expanding the microwave absorption application of cerium oxide nanocomposite materials.

Description of drawings

Fig. 1 is the XRD spectrum of the reduced graphene oxide/cerium oxide nanocomposite material of the present invention.

Fig. 2 is the TEM photo of the reduced graphene oxide/cerium oxide nanocomposite material of the present invention.

Fig. 3 is the electromagnetic wave reflection loss spectrum of the reduced graphene oxide/cerium oxide nanocomposite material of the present invention.

Figure 4 is a comparison map of electromagnetic wave reflection loss between the reduced graphene oxide/cerium oxide nanocomposite material of the present invention and pure cerium oxide nanoparticles (the thickness of the sample coating is 2.0 mm).

detailed description

Below in conjunction with embodiment, the present invention will be further described.

The raw materials used and their sources are as follows:

(1) Natural graphite flakes: 325 mesh, purity ≥99%, Qingdao Huatai Durable Sealing Co., Ltd.

(2) Potassium permanganate: Purity AR, Sinopharm Chemical Reagent Co., Ltd.

(3) Hydrogen peroxide: Purity AR, Sinopharm Chemical Reagent Co., Ltd.

(4) Concentrated sulfuric acid: purity 95-98%, Tianjin Bodi Chemical Co., Ltd.

(5) Concentrated phosphoric acid: purity ≥85%, Tianjin Bodi Chemical Co., Ltd.

(6) Hydrochloric acid: purity 36-38%, Tianjin Bodi Chemical Co., Ltd.

(7) Ammonia water: 25% purity, Sinopharm Chemical Reagent Co., Ltd.

(8) Cerium nitrate hexahydrate: Purity AR, Aladdin's reagent

(9) Ethanol: Purity AR, Sinopharm Chemical Reagent Co., Ltd.

The specific operation steps for preparing the composite microwave absorbing material of reduced graphene oxide and nano-cerium oxide are as follows:

(1) Preparation of graphite oxide

Graphite oxide was prepared by the improved Hummers method, 3g of graphite powder and 2g of sodium nitrate (NaNO ₃ ) were added to a 250mL beaker, and 70mL of concentrated sulfuric acid with a concentration of 95-98% was slowly added along the wall of the beaker and stirred evenly. Under the condition of ice bath, 10 g of potassium permanganate (KMnO ₄ ) was divided into 5 equal parts, added in 5 times at intervals of 10 minutes, and stirred for one hour. Afterwards, the ice-water bath was removed, and stirred in a 35°C water bath for 2 h. After stirring, 140 mL of deionized water was slowly added to the mixed solution and stirred for 15 min. At this time, the temperature of the system was raised to about 90 °C, and then 30% hydrogen peroxide (H ₂ O ₂ ) was added dropwise until the reaction liquid turned bright yellow. After the reaction, the reaction solution was filtered while it was hot, and washed with 1:10 dilute hydrochloric acid (prepared from 500 mL deionized water and 50 mL concentrated hydrochloric acid with a concentration of 36-38%) to remove excess metal ions. The product was centrifuged at high speed and washed repeatedly until the pH was 7. Finally, the product was freeze-dried for 48 h to obtain graphite oxide.

(2) Preparation of microwave absorbing materials composited by reduced graphene oxide and nano-cerium oxide

Dissolve 20 mg of graphite oxide in 60 mL of deionized water, disperse ultrasonically for 1 h, and the power of ultrasonic radiation is 180 W, and obtain 60 mL of brown-yellow graphene oxide solution. Weigh 0.5 g of cerium nitrate hexahydrate (Ce(NO ₃ ) ₃ ·6H ₂ O) into 60 mL of graphene oxide solution, and stir magnetically. After the cerium nitrate hexahydrate is completely dissolved, slowly add 3 mL of ammonia solution with a concentration of 25-28% to the reaction solution under the action of ultrasound. At this time, the pH of the reaction solution is about 10, the ultrasonic radiation power is 180W, and the ultrasonic treatment time is 30min. The reaction liquid was transferred to a 100mL hydrothermal reaction kettle, and hydrothermally reacted at 180 ^˚C for 24h. After the reaction, the product is purified by centrifugation, washing with water, washing with ethanol and the like. Finally, vacuum drying at 60˚C for 24 h to obtain a microwave absorbing material composited with reduced graphene oxide and nano-cerium oxide.

The microwave absorbing material composed of reduced graphene oxide and nano-cerium oxide can be used as an excellent microwave absorber, and its microwave absorbing performance parameters are obtained by the following detection methods:

Mix the microwave absorbing material composed of reduced graphene oxide and nano-cerium oxide with paraffin (the volume fraction of the composite microwave absorbing material accounts for 30%), keep warm at 80˚C for half an hour to melt the paraffin, stir evenly, put it into a mold, and Under the pressure of 2 Mpa, a coaxial ring with an inner diameter of 3.04 mm and an outer diameter of 7.00 mm was made, and its thickness was ground to 2 mm. The imaginary part, the reflection loss of the composite material is calculated by classical coaxial line theory.

After testing, pure cerium oxide nanoparticles have almost no microwave absorption properties. However, the microwave absorbing material composited with reduced graphene oxide and nano cerium oxide of the present invention has excellent microwave absorbing properties. The reflection loss at the frequency of 4.3～17GHz is -32～-10dB (electromagnetic wave absorption is more than 90%); the microwave reflection loss reaches the maximum at 17GHz, which is -32dB; when the coating thickness is 2.0mm, the reflection loss is low The frequency bandwidth at -10dB (electromagnetic wave absorption is more than 90%) is 4.3 GHz.

Claims (3)

1. a composite microwave absorbing material of reduced graphene oxide and nanometer cerium oxide is characterized in that: graphite oxide is prepared with improved Hummers method, graphene oxide solution is mixed with cerium nitrate hexahydrate in a mass ratio of 1:25, adjusted The pH value is 10, and a one-step hydrothermal method is used to reduce graphene oxide while generating nano-cerium oxide to obtain a composite microwave absorbing material of reduced graphene oxide and nano-cerium oxide; The composite microwave absorbing material is characterized in that: the surface of the reduced graphite oxide flakes is evenly loaded with nanometer cerium oxide particles, and adjacent flakes are separated from each other, forming a layered sandwich structure, which helps to improve the microwave absorbing performance; The average nanoparticle size of the nano-cerium oxide is 15nm, which has a prominent quantum size effect and an excellent oxygen vacancy effect; The weight ratio of reduced graphene oxide and nano cerium oxide in the composite microwave absorbing material is 1:10; When the composite microwave absorbing material is a coating with a thickness of 1.5~4.0mm, the reflection loss at the frequency of 4.3~17GHz is -32~-10dB; the electromagnetic wave absorption is over 90%. 2. prepare the method for the composite microwave absorbing material of a kind of reduced graphene oxide and nano cerium oxide described in claim 1, it is characterized in that concrete operation steps are as follows: (1) Preparation of graphite oxide by improved Hummers method Take 3g of graphite powder and 2g of sodium nitrate into a 250mL beaker, slowly add 70mL along the wall of the cup Concentrated sulfuric acid with a concentration of 95~98% and stirred evenly; under the condition of ice bath, add 10g of potassium permanganate in 5 times, the amount of each addition is 2g, and stir for one hour; stir in a 35˚C water bath for 2h, Obtain a mixed solution; slowly add 140mL deionized water into the mixed solution and stir for 15min, at this time the temperature of the system is raised to 88～92˚C, and the hydrogen peroxide with a concentration of 30% is added dropwise until the reaction solution turns bright yellow; The solution was filtered while it was hot, and washed with a 1:10 dilute hydrochloric acid solution to remove excess metal ions; high-speed centrifugation and repeated water washing until the pH value was 7; freeze-dried for 48 hours to obtain graphite oxide; (2) Preparation of microwave absorbing materials composited by reduced graphene oxide and nano-cerium oxide Dissolve 20mg of graphite oxide in 60mL of deionized water and disperse it ultrasonically for 1 hour to obtain 60mL of brown-yellow graphene oxide solution; take 0.5g of cerium nitrate hexahydrate and add it to 60mL of graphene oxide solution, and stir magnetically; The cerium nitrate is completely dissolved, and slowly add 3 mL of ammonia solution with a concentration of 25-28% to the reaction solution dropwise under the action of ultrasound. At this time, the pH value of the reaction solution is 9-11; ^˚C hydrothermal reaction for 24 hours; centrifugation, water washing, ethanol washing and purification; vacuum drying at 60˚C for 24 hours to obtain a microwave absorbing material composited with reduced graphene oxide and nano-cerium oxide. 3. According to claim 2, the preparation method of the microwave absorbing material composited by reduced graphene oxide and nano-cerium oxide is characterized in that: in the preparation process of the hydrothermal precursor in step (2), the ultrasonic radiation power is 180 W, and the ultrasonic radiation power is 180 W. The processing time is 30 min.