A NiCo2O4@SiO2 / GNs microwave absorbing material and its preparation method

Abstract

The application discloses a kind of NiCo2O4@SiO2 / GNs wave-absorbing materials and preparation method thereof, comprising the following preparation steps: (1) with nickel salt and cobalt salt as raw material under the action of urea, NiCo2O4 Nanorod is generated;(2) with tetraethyl orthosilicate as precursor, NiCo2O4@SiO2 Material is prepared by in-situ reaction;(3) the prepared NiCo2O4@SiO2 With graphene nanosheet (GNs) hydrothermal reaction is carried out, and NiCo2O4@SiO2 / GNs wave-absorbing material is prepared.The SiO2 of NiCo2O4@SiO2 / GNs wave-absorbing material of the application as NiCo2O4 magnetic core and graphene nanosheet conductive shell between bridge or buffer layer, play good cooperation between magnetic and dielectric structure, show better wave-absorbing performance and impedance matching performance, can obtain excellent electromagnetic wave absorption performance, with good application prospect in electromagnetic wave absorption material field.

Description

Technical Field

[0001] This invention relates to the field of microwave absorbing technology, specifically to a NiCo2O4@SiO2 / GNs microwave absorbing material and its preparation method. Background Technology

[0002] In recent years, with the continuous development of science and technology, electromagnetic waves have been widely used as a transmission medium. However, electromagnetic pollution caused by electromagnetic waves has seriously damaged the ecological environment and threatened people's health. The application of absorbing materials is an effective means to prevent electromagnetic pollution, achieve radar stealth, and electromagnetic compatibility. It has extremely wide applications in both civilian and military fields. Absorbing materials are a class of materials that can absorb the energy of electromagnetic waves projected onto their surface. The basic conditions for materials to absorb electromagnetic waves are: (1) When electromagnetic waves are incident on the material, they can enter the interior of the material to the maximum extent, that is, the material is required to have matching characteristics; (2) The electromagnetic waves that enter the interior of the material can be rapidly and almost completely attenuated, that is, attenuation characteristics.

[0003] Currently, microwave absorbing materials are developing towards being "thin, light, wide, and strong." However, single-component microwave absorbing materials cannot simultaneously meet these requirements. Composite microwave absorbing materials, on the other hand, can overcome the shortcomings of single-component materials and have considerable advantages, making them one of the future development directions for microwave absorbing materials. Graphene, composed of a single layer of carbon atoms, is the thinnest two-dimensional nanomaterial in the world. It possesses superior optical, electrical, and mechanical properties not found in conventional carbon materials, making it a microwave absorbing material with great potential. However, due to its extremely weak magnetic loss, the microwave absorption effect of graphene alone is very poor. But by combining graphene with other materials with good magnetic properties, the impedance matching problem can be significantly improved, achieving superior microwave absorption performance. Spinel-type NiCo2O4 has advantages such as a porous structure, high polarization and high loss, and large shape anisotropy, making it one of the most promising microwave absorbing materials. However, exposed NiCo2O4 nanorods have disadvantages such as magnetic aggregation, high density, and easy oxidation. Multilevel core-shell morphology can effectively "wrap" the magnetic core, thereby effectively solving these problems. Among known transparent dielectric materials, SiO2 is one of the most popular due to its excellent dielectric and optical properties. The ease of functionalization of SiO2 further facilitates the docking of functional sites in multi-level components. As a bridge or buffer layer between magnetic cores and conductive shell graphene nanosheets, SiO2 exhibits good synergy between magnetic and dielectric components in the nanostructure, which can improve the material's microwave absorption performance.

[0004] In order to improve the shortcomings of single absorbing materials, the inventors of this invention have put forward this invention after a long period of research and practice. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a NiCo2O4@SiO2 / GNs microwave absorbing material and its preparation method, employing the following technical solution:

[0006] A method for preparing NiCo2O4@SiO2 / GNs microwave absorbing material, characterized by comprising the following preparation steps:

[0007] (1) Preparation of NiCo2O4: Nickel salt and cobalt salt were dissolved in a mixed solution of deionized water and ethylene glycol and stirred magnetically until completely dissolved. Urea was added to the mixed solution and stirring was continued for 0.5 h to 1 h to form a homogeneous mixture. The mixture was transferred to a high-pressure reactor lined with polytetrafluoroethylene for hydrothermal reaction. After the reaction was completed, the product was collected by centrifugation. The product was washed three times with deionized water and anhydrous ethanol and dried in a drying oven at 60 °C for 6 h. The dried product was calcined at 380 °C for 4 h to obtain NiCo2O4 nanorods.

[0008] (2) Preparation of NiCo2O4@SiO2: NiCo2O4 nanorods were ultrasonically dispersed in a mixed solution of ethanol and ammonia. Then, tetraethyl orthosilicate (TEOS) was added dropwise under vigorous stirring at room temperature. Then, an equal amount of (3-aminopropyl)trimethoxysilane (APTMS) was added. After stirring continuously for 12 h, the product was collected by centrifugation after the reaction was completed. The product was washed three times with deionized water and anhydrous ethanol and dried under vacuum at 60 °C for 6 h to obtain NiCo2O4@SiO2.

[0009] (3) Preparation of NiCo2O4@SiO2 / GNs: The obtained NiCo2O4@SiO2 was dissolved in ethylene glycol and stirred to form a uniform mixed solution. GNs were added to the uniform mixed solution, stirred evenly, and then sonicated for 0.5 h. Then it was transferred to a high-pressure reactor with a polytetrafluoroethylene liner for hydrothermal reaction. After the reaction was completed, the product was collected by centrifugation. The product was washed three times with deionized water and anhydrous ethanol and dried in a drying oven at 60 °C for 6 h under vacuum to obtain NiCo2O4@SiO2 / GNs.

[0010] Furthermore, in step (1), the nickel salt is one of Ni(NO3)2·6H2O, NiCl2·6H2O, and (CH3COO)2Ni·4H2O, and the cobalt salt is one of Co(NO3)2·6H2O, CoCl2·6H2O, and (CH3COO)2Co·4H2O.

[0011] Furthermore, in step (1), the volume ratio of deionized water to ethylene glycol is 1:(1-5).

[0012] Furthermore, in step (1), the molar ratio of nickel salt, cobalt salt and urea is 1:2:(10-60).

[0013] Furthermore, in step (1), the temperature of the hydrothermal reaction is 100℃~160℃ and the time is 4h~8h.

[0014] Furthermore, in step (2), the volume ratio of ethanol to ammonia solution is 9:1.

[0015] Furthermore, in step (2), the molar ratio of NiCo2O4 nanorods to TEOS is 1:(5-15).

[0016] Furthermore, in step (3), the mass ratio of NiCo2O4@SiO2 to GNs is 1:(4-19).

[0017] Furthermore, in step (3), GNs are obtained by acidifying graphene nanosheets with concentrated nitric acid at a concentration of 60% to 70% for 18 to 22 hours; the sheet size of the GNs is 0.5 μm to 3 μm, the thickness of a single sheet is 0.55 nm to 3.74 nm, and the number of sheets is <10.

[0018] Furthermore, the conditions for the hydrothermal reaction in step (3) are: reaction temperature of 140℃~200℃ and reaction time of 8h~20h.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] (1) The NiCo2O4@SiO2 / GNs absorbing material of the present invention has dual absorbing properties of dielectric loss and magnetic loss. Spinel NiCo2O4 not only has magnetic loss capability, but also has strong dielectric loss capability. The defect-induced polarization loss mechanism in the material can be adjusted by controlling the concentration of oxygen vacancies in NiCo2O4.

[0021] (2) SiO2 as a coating material can better solve the problem of uneven magnetic aggregation and dispersion of NiCo2O4. At the same time, SiO2, as a bridge or buffer layer between the magnetic core and the conductive shell graphene nanosheet, has good synergy between the magnetic and dielectric components in the nanostructure, which can improve the wave absorption performance of the material. Attached Figure Description

[0022] The above and other objects, features and advantages of the present invention will become more apparent from the following description of embodiments of the invention with reference to the accompanying drawings, in which:

[0023] Figure 1 This is a graph showing the electromagnetic wave absorption performance of the material of this invention. Detailed Implementation

[0024] The present invention will be further described in detail below through specific embodiments, but it should not be construed as limiting the scope of the invention to the following examples. Various substitutions or modifications made based on ordinary technical knowledge and conventional methods in the art without departing from the above-described methodological spirit of the invention should be included within the scope of the invention. Example 1

[0025] This embodiment provides a method for preparing NiCo2O4@SiO2 / GNs microwave absorbing material, characterized by the following preparation steps:

[0026] (1) Preparation of NiCo2O4: 0.1 mol of Ni(NO3)2·6H2O and 0.2 mol of Co(NO3)2·6H2O were accurately weighed according to the stoichiometric ratio and dissolved in a mixed solution of 100 ml of deionized water and 100 ml of ethylene glycol. The mixture was magnetically stirred until completely dissolved. 1 mol of urea was added to the mixed solution and stirred for 0.5 h to form a homogeneous mixture. The mixture was transferred to a high-pressure reactor lined with polytetrafluoroethylene for hydrothermal reaction at a temperature of 100 °C for 8 h. After the reaction, the product was collected by centrifugation. The product was washed three times with deionized water and anhydrous ethanol and dried in a drying oven at 60 °C for 6 h. The dried product was calcined at 380 °C for 4 h to obtain NiCo2O4 nanorods.

[0027] (2) Preparation of NiCo2O4@SiO2: 0.1 mol of NiCo2O4 nanorods were ultrasonically dispersed in a mixed solution consisting of 270 ml of ethanol and 30 ml of ammonia. Then, 0.5 mol of tetraethyl orthosilicate (TEOS) was added dropwise under vigorous stirring at room temperature. Then, an equal amount of (3-aminopropyl)trimethoxysilane (APTMS) was added. After stirring continuously for 12 h, the product was collected by centrifugation after the reaction was completed. The product was washed three times with deionized water and anhydrous ethanol and dried under vacuum at 60 °C for 6 h to obtain NiCo2O4@SiO2.

[0028] (3) Preparation of NiCo2O4@SiO2 / GNs: 10 mg of the prepared NiCo2O4@SiO2 was dissolved in 200 ml of ethylene glycol and stirred to form a uniform mixed solution. 40 mg of GNs was added to the uniform mixed solution and stirred evenly. The mixture was then sonicated for 0.5 h and then transferred to a high-pressure reactor with a polytetrafluoroethylene liner for hydrothermal reaction. The hydrothermal reaction temperature was 140 °C and the reaction time was 20 h. After the reaction was completed, the product was collected by centrifugation. The product was washed three times with deionized water and anhydrous ethanol and dried in a drying oven at 60 °C for 6 h under vacuum to obtain NiCo2O4@SiO2 / GNs.

[0029] The GNs are obtained by acidifying graphene nanosheets with concentrated nitric acid at a concentration of 60% for 22 hours; the sheet size of the GNs is 0.5μm to 3μm, the thickness of a single sheet is 0.55nm to 3.74nm, and the number of sheets is <10. Example 2

[0030] This embodiment provides a method for preparing NiCo2O4@SiO2 / GNs microwave absorbing material, characterized by the following preparation steps:

[0031] (1) Preparation of NiCo2O4: 0.1 mol of NiCl2·6H2O and 0.2 mol of CoCl2·6H2O were accurately weighed according to the stoichiometric ratio and dissolved in a mixed solution of 100 ml of deionized water and 200 ml of ethylene glycol. The solution was magnetically stirred until completely dissolved. 3 mol of urea was added to the mixed solution and stirred for 1 h to form a homogeneous mixture. The mixture was transferred to a high-pressure reactor lined with polytetrafluoroethylene for hydrothermal reaction at a temperature of 130 °C for 6 h. After the reaction, the product was collected by centrifugation. The product was washed three times with deionized water and anhydrous ethanol and dried in a drying oven at 60 °C for 6 h. The dried product was calcined at 380 °C for 4 h to obtain NiCo2O4 nanorods.

[0032] (2) Preparation of NiCo2O4@SiO2: 0.1 mol of NiCo2O4 nanorods were ultrasonically dispersed in a mixed solution consisting of 270 ml of ethanol and 30 ml of ammonia. Then, 0.8 mol of tetraethyl orthosilicate (TEOS) was added dropwise under vigorous stirring at room temperature. Then, an equal amount of (3-aminopropyl)trimethoxysilane (APTMS) was added. After stirring continuously for 12 h, the product was collected by centrifugation after the reaction was completed. The product was washed three times with deionized water and anhydrous ethanol and dried under vacuum at 60 °C for 6 h to obtain NiCo2O4@SiO2.

[0033] (3) Preparation of NiCo2O4@SiO2 / GNs: 10 mg of the prepared NiCo2O4@SiO2 was dissolved in 200 ml of ethylene glycol and stirred to form a uniform mixed solution. 100 mg of GNs was added to the uniform mixed solution and stirred evenly. The mixture was then sonicated for 0.5 h and then transferred to a high-pressure reactor with a polytetrafluoroethylene liner for hydrothermal reaction. The hydrothermal reaction temperature was 160 °C and the reaction time was 16 h. After the reaction was completed, the product was collected by centrifugation. The product was washed three times with deionized water and anhydrous ethanol and dried under vacuum at 60 °C for 6 h in a drying oven to obtain NiCo2O4@SiO2 / GNs.

[0034] The GNs are obtained by acidifying graphene nanosheets with concentrated nitric acid at a concentration of 70% for 22 hours; the sheet size of the GNs is 0.5μm to 3μm, the thickness of a single sheet is 0.55nm to 3.74nm, and the number of sheets is <10. Example 3

[0035] This embodiment provides a method for preparing NiCo2O4@SiO2 / GNs microwave absorbing material, characterized by the following preparation steps:

[0036] (1) Preparation of NiCo2O4: 0.1 mol of (CH3COO)2Ni·4H2O and 0.2 mol of (CH3COO)2Co·4H2O were accurately weighed according to the stoichiometric ratio and dissolved in a mixed solution of 100 ml deionized water and 400 ml ethylene glycol. The mixture was magnetically stirred until completely dissolved. 6 mol of urea was added to the mixed solution and stirred for 1 h to form a homogeneous mixture. The mixture was transferred to a high-pressure reactor lined with polytetrafluoroethylene for hydrothermal reaction at a temperature of 140 °C for 5 h. After the reaction, the product was collected by centrifugation. The product was washed three times with deionized water and anhydrous ethanol and dried under vacuum at 60 °C for 6 h in a drying oven. The dried product was calcined at 380 °C for 4 h to obtain NiCo2O4 nanorods.

[0037] (2) Preparation of NiCo2O4@SiO2: 0.1 mol of NiCo2O4 nanorods were ultrasonically dispersed in a mixed solution consisting of 270 ml of ethanol and 30 ml of ammonia. Then, 1 mol of tetraethyl orthosilicate (TEOS) was added dropwise under vigorous stirring at room temperature. Then, an equal amount of (3-aminopropyl)trimethoxysilane (APTMS) was added. After stirring continuously for 12 h, the product was collected by centrifugation after the reaction was completed. The product was washed three times with deionized water and anhydrous ethanol and dried under vacuum at 60 °C for 6 h to obtain NiCo2O4@SiO2.

[0038] (3) Preparation of NiCo2O4@SiO2 / GNs: 10 mg of the prepared NiCo2O4@SiO2 was dissolved in 300 ml of ethylene glycol and stirred to form a uniform mixed solution. 90 mg of GNs was added to the uniform mixed solution and stirred evenly. The mixture was then sonicated for 0.5 h and then transferred to a high-pressure reactor with a polytetrafluoroethylene liner for hydrothermal reaction. The hydrothermal reaction temperature was 180 °C and the reaction time was 12 h. After the reaction was completed, the product was collected by centrifugation. The product was washed three times with deionized water and anhydrous ethanol and dried in a drying oven at 60 °C under vacuum for 6 h to obtain NiCo2O4@SiO2 / GNs.

[0039] The GNs are obtained by acidifying graphene nanosheets with concentrated nitric acid at a concentration of 60% for 22 hours; the sheet size of the GNs is 0.5μm to 3μm, the thickness of a single sheet is 0.55nm to 3.74nm, and the number of sheets is <10. Example 4

[0040] This embodiment provides a method for preparing NiCo2O4@SiO2 / GNs microwave absorbing material, characterized by the following preparation steps:

[0041] (1) Preparation of NiCo2O4: 0.1 mol of Ni(NO3)2·6H2O and 0.2 mol of Co(NO3)2·6H2O were accurately weighed according to the stoichiometric ratio and dissolved in a mixed solution of 100 ml deionized water and 500 ml ethylene glycol. The solution was magnetically stirred until completely dissolved. 4 mol of urea was added to the mixed solution and stirred for 1 h to form a homogeneous mixture. The mixture was transferred to a high-pressure reactor lined with polytetrafluoroethylene for hydrothermal reaction at 160 °C for 4 h. After the reaction, the product was collected by centrifugation. The product was washed three times with deionized water and anhydrous ethanol and dried in a drying oven at 60 °C for 6 h. The dried product was calcined at 380 °C for 4 h to obtain NiCo2O4 nanorods.

[0042] (2) Preparation of NiCo2O4@SiO2: 0.1 mol of NiCo2O4 nanorods were ultrasonically dispersed in a mixed solution consisting of 270 ml of ethanol and 30 ml of ammonia. Then, 1.5 mol of tetraethyl orthosilicate (TEOS) was added dropwise under vigorous stirring at room temperature. Then, an equal amount of (3-aminopropyl)trimethoxysilane (APTMS) was added. After stirring continuously for 12 h, the product was collected by centrifugation after the reaction was completed. The product was washed three times with deionized water and anhydrous ethanol and dried under vacuum at 60 °C for 6 h to obtain NiCo2O4@SiO2.

[0043] (3) Preparation of NiCo2O4@SiO2 / GNs: 10 mg of the prepared NiCo2O4@SiO2 was dissolved in 300 ml of ethylene glycol and stirred to form a uniform mixed solution. 190 mg of GNs was added to the uniform mixed solution and stirred evenly. The mixture was then sonicated for 0.5 h and then transferred to a high-pressure reactor with a polytetrafluoroethylene liner for hydrothermal reaction. The hydrothermal reaction temperature was 200 °C and the reaction time was 8 h. After the reaction was completed, the product was collected by centrifugation. The product was washed three times with deionized water and anhydrous ethanol and dried in a drying oven at 60 °C under vacuum for 6 h to obtain NiCo2O4@SiO2 / GNs.

[0044] The GNs are obtained by acidifying graphene nanosheets with concentrated nitric acid at a concentration of 70% for 22 hours; the sheet size of the GNs is 0.5μm to 3μm, the thickness of a single sheet is 0.55nm to 3.74nm, and the number of sheets is <10.

[0045] The absorption performance parameters of the absorbing materials in the above four embodiments were measured using a vector network analyzer in the frequency range of 2 GHz to 18 GHz. The test results are as follows: Figure 1 As shown.

[0046] The test results show that the absorbing materials of the four embodiments of the present invention all have good absorption performance. In embodiment 2, the absorption performance reaches -50dB, and the effective absorption bandwidth of less than -10dB is 6.03GHz (11.76GHz~17.79GHz). In embodiment 3, the absorption performance reaches -46.8dB, and the effective absorption bandwidth of less than -10dB is 6.05GHz (10.18GHz~16.23GHz).

[0047] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a NiCo2O4@SiO2 / GNs microwave absorbing material, characterized in that, The preparation steps include the following: (1) Preparation of NiCo2O4: Nickel salt and cobalt salt were dissolved in a mixed solution of deionized water and ethylene glycol and stirred magnetically until completely dissolved. Urea was added to the mixed solution and stirring was continued for 0.5 h to 1 h to form a homogeneous mixture. The mixture was transferred to a high-pressure reactor lined with polytetrafluoroethylene for hydrothermal reaction. After the reaction was completed, the product was collected by centrifugation. The product was washed three times with deionized water and anhydrous ethanol and dried in a drying oven at 60 °C for 6 h. The dried product was calcined at 380 °C for 4 h to obtain NiCo2O4 nanorods. (2) Preparation of NiCo2O4@SiO2: NiCo2O4 nanorods were ultrasonically dispersed in a mixed solution of ethanol and ammonia. Then, tetraethyl orthosilicate (TEOS) was added dropwise under vigorous stirring at room temperature. Then, an equal amount of 3-aminopropyltrimethoxysilane (APTMS) was added. After stirring continuously for 12 h, the product was collected by centrifugation after the reaction was completed. The product was washed three times with deionized water and anhydrous ethanol and dried under vacuum at 60 °C for 6 h to obtain NiCo2O4@SiO2. (3) Preparation of NiCo2O4@SiO2 / GNs: The obtained NiCo2O4@SiO2 was dissolved in ethylene glycol and stirred to form a uniform mixed solution. GNs were added to the uniform mixed solution, stirred evenly, and then sonicated for 0.5 h. Then it was transferred to a high-pressure reactor with a polytetrafluoroethylene liner for hydrothermal reaction. After the reaction was completed, the product was collected by centrifugation. The product was washed three times with deionized water and anhydrous ethanol and dried in a drying oven at 60 °C for 6 h under vacuum to obtain NiCo2O4@SiO2 / GNs.

2. The preparation method of the NiCo2O4@SiO2 / GNs microwave absorbing material according to claim 1, characterized in that, In step (1), the nickel salt is one of Ni(NO3)2·6H2O, NiCl2·6H2O, and (CH3COO)2Ni·4H2O, and the cobalt salt is one of Co(NO3)2·6H2O, CoCl2·6H2O, and (CH3COO)2Co·4H2O.

3. The method for preparing the NiCo2O4@SiO2 / GNs microwave absorbing material according to claim 1, characterized in that, In step (1), the volume ratio of deionized water to ethylene glycol is 1:(1-5).

4. The method for preparing the NiCo2O4@SiO2 / GNs microwave absorbing material according to claim 1, characterized in that, In step (1), the molar ratio of nickel salt, cobalt salt and urea is 1:2:(10-60).

5. The preparation method of the NiCo2O4@SiO2 / GNs microwave absorbing material according to claim 1, characterized in that, In step (1), the temperature of the hydrothermal reaction is 100℃~160℃ and the time is 4h~8h.

6. The method for preparing the NiCo2O4@SiO2 / GNs microwave absorbing material according to claim 1, characterized in that, In step (2), the volume ratio of ethanol to ammonia solution is 9:

1.

7. The method for preparing the NiCo2O4@SiO2 / GNs microwave absorbing material according to claim 1, characterized in that, In step (2), the molar ratio of NiCo2O4 nanorods to TEOS is 1:(5-15).

8. The method for preparing the NiCo2O4@SiO2 / GNs microwave absorbing material according to claim 1, characterized in that, In step (3), the mass ratio of NiCo2O4@SiO2 to GNs is 1:(4-19).

9. The method for preparing the NiCo2O4@SiO2 / GNs microwave absorbing material according to claim 1, characterized in that, In step (3), GNs are obtained by acidifying graphene nanosheets with concentrated nitric acid at a concentration of 60% to 70% for 18 to 22 hours. The sheet size of the GNs is 0.5 μm to 3 μm, the thickness of a single sheet is 0.55 nm to 3.74 nm, and the number of sheets is <10.

10. The method for preparing the NiCo2O4@SiO2 / GNs microwave absorbing material according to claim 1, characterized in that, The conditions for the hydrothermal reaction in step (3) are: reaction temperature of 140°C to 200°C and reaction time of 8h to 20h.

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