A zinc oxide-based electromagnetic wave absorbing material and its preparation method and application

Abstract

The present invention belongs to the technical field of electromagnetic wave absorbing materials and discloses a zinc oxide-based electromagnetic wave absorbing material, its preparation method, and application. The zinc oxide-based electromagnetic wave absorbing material has core-shell morphology and rod-like structure characteristics. The core is composed of ZnO and the shell is composed of NiCo2O4, and the NiCo2O4 is in the form of nanosheets. The zinc oxide-based electromagnetic wave absorbing material of the present invention optimizes the microstructure of the obtained sample by regulating the mass ratio of ZnO and metal ions. The resulting core-shell structure product can not only optimize the structure but also improve the impedance matching of the material. The core-shell structure of the zinc oxide-based electromagnetic wave absorbing material increases the heterojunction interface of the material, scattering and reflecting a large amount of incident electromagnetic waves, thereby improving the electromagnetic wave absorbing performance of the material.

Description

Technical Field

[0001] The present invention belongs to the technical field of electromagnetic wave absorbing materials, and in particular relates to a zinc oxide-based electromagnetic wave absorbing material and a preparation method and application thereof. Background Art

[0002] The rapid development of electronic devices and wireless communications has made people's daily lives more intelligent and greatly satisfied people's needs. However, they inevitably cause a large amount of electromagnetic pollution, which can lead to electronic device failures, damage to human organs, and other negative effects. Advanced electromagnetic wave absorbing materials are needed to reduce or eliminate electromagnetic radiation. The mechanisms of electromagnetic wave absorption are dielectric loss and magnetic loss, which are the most important for the design of electromagnetic wave absorbing materials. In principle, high-performance electromagnetic wave absorbing materials must have excellent impedance matching and strong attenuation capabilities. In addition, wide bandwidth, light weight, and thin thickness are the basic factors for ideal electromagnetic wave absorbing materials.

[0003] Zinc oxide (ZnO) is a semiconductor material with excellent mechanical properties, wide bandgap and non-toxicity, which has attracted great interest in the field of electromagnetic wave absorption. However, due to its poor impedance matching, single ZnO cannot be directly used for microwave absorption. Generally, it is a wise strategy to combine ZnO with other electromagnetic wave absorbing materials through reasonable microstructure to obtain advanced electromagnetic wave absorbing materials. At present, the preparation of ZnO-based electromagnetic wave materials is relatively common, but there are still problems such as complex preparation process, high preparation cost and large amount of waste liquid generated during the preparation process, which pollutes the environment. At the same time, the prepared electromagnetic wave absorbing materials also have problems such as poor absorption performance, narrow effective absorption bandwidth and large loading capacity.

[0004] Therefore, it is of great significance to develop an electromagnetic absorbing material with better performance, or an absorbing material with low preparation cost, environmental friendliness and no pollution. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention proposes a zinc oxide-based electromagnetic wave absorbing material, a preparation method thereof, and an application thereof. The zinc oxide-based electromagnetic wave absorbing material of the present invention has the excellent properties of good wave absorbing performance and a wide effective absorption bandwidth, and further has the advantage of a small load. Moreover, the preparation method of the present invention has low preparation cost, is environmentally friendly and pollution-free. During the synthesis process, the present invention does not use organic solvents such as DMF (N,N-dimethylformamide) and methanol, but uses deionized water and ethanol as solvents, which reduces the cost to a certain extent and does not produce waste liquid harmful to the environment. The present invention adopts a simple hydrothermal method and annealing process to prepare the zinc oxide-based electromagnetic wave absorbing material, and the annealing temperature is 400°C, which greatly simplifies the preparation process.

[0006] A first aspect of the present invention provides a zinc oxide-based electromagnetic wave absorbing material.

[0007] Specifically, a zinc oxide-based electromagnetic wave absorbing material has core-shell morphology and rod-like structure characteristics, wherein the core comprises ZnO, the shell comprises NiCo2O4, and the NiCo2O4 is in the form of nanosheets.

[0008] In the zinc oxide-based electromagnetic wave absorbing material, NiCo2O4 nanosheets are uniformly and densely grown on the surface of the rod-shaped ZnO, which can be recorded as ZnO / NiCo2O4. The zinc oxide-based electromagnetic wave absorbing material has a rod-shaped structural feature as a whole.

[0009] Preferably, the aspect ratio of the zinc oxide-based electromagnetic wave absorbing material is 1:(2-7); further preferably, the aspect ratio of the zinc oxide-based electromagnetic wave absorbing material is 1:(3-7).

[0010] Preferably, the zinc oxide-based electromagnetic wave absorbing material has a length of 1-5 μm and a diameter of 100-600 nm; further preferably, the zinc oxide-based electromagnetic wave absorbing material has a length of 1-3 μm and a diameter of 200-600 nm.

[0011] Preferably, the minimum reflection loss of the zinc oxide-based electromagnetic wave absorbing material may be less than -55 dB, for example, -59.93 dB.

[0012] Preferably, the effective absorption bandwidth of the zinc oxide-based electromagnetic wave absorbing material is 10.96-17.36 GHz. A minimum reflection loss RLmin of less than -10 dB is considered effective absorption.

[0013] A second aspect of the present invention provides a method for preparing a zinc oxide-based electromagnetic wave absorbing material.

[0014] Specifically, a method for preparing a zinc oxide-based electromagnetic wave absorbing material comprises the following steps:

[0015] Rod-shaped ZnO is dispersed in a mixed solution of deionized water and alcohol, ultrasonically dispersed, and then nickel salt, cobalt salt and hexamethylenetetramine are added. The mixture is kept warm, cooled, and separated to obtain the precursor ZnO / NiCo(OH) x , the X is greater than 0;

[0016] The precursor ZnO / NiCo(OH) x Annealing treatment is performed to obtain the zinc oxide-based electromagnetic wave absorbing material.

[0017] Preferably, the alcohol comprises ethanol or propanol; preferably ethanol.

[0018] Preferably, the ultrasonic dispersion time is 1-2 hours, preferably 1.5-2 hours.

[0019] Preferably, the nickel salt is selected from at least one of nickel nitrate, nickel chloride or nickel sulfate; further preferably, the nickel salt is nickel nitrate or nickel nitrate hexahydrate.

[0020] Preferably, the cobalt salt is selected from at least one of cobalt nitrate, cobalt chloride or cobalt sulfate; further preferably, the cobalt salt is cobalt nitrate or cobalt nitrate hexahydrate.

[0021] Preferably, the temperature of the heat preservation is 30-90° C. More preferably, the temperature of the heat preservation is 50-90° C. The heat preservation process can be performed by a hydrothermal method.

[0022] Preferably, the insulation time is 1-48 hours; further preferably, the insulation time is 6-10 hours.

[0023] Preferably, the mass ratio of the rod-shaped ZnO, nickel salt, cobalt salt and hexamethylenetetramine is (0.1-3): (0.2-4): (0.3-6): 3.1; further preferably, the mass ratio of the rod-shaped ZnO, nickel salt, cobalt salt and hexamethylenetetramine is (0.1-2): (0.3-2): (0.6-4): 3.1.

[0024] Preferably, the annealing treatment is performed under the protection of an inert gas, which may be nitrogen or argon.

[0025] Preferably, the heating rate during the annealing process is 1-30°C·min -1 ; The preferred heating rate is 5-10℃·min -1 .

[0026] Preferably, the temperature during the annealing process is raised to 300-1000°C; preferably 300-400°C.

[0027] Preferably, the annealing treatment time is 1-15 hours, preferably 1-3 hours.

[0028] Preferably, the rod-shaped ZnO is prepared by stirring and mixing zinc salt, hexamethylenetetramine and water, and then heat-insulating, cooling, washing and drying to obtain the rod-shaped ZnO.

[0029] Preferably, the zinc salt includes at least one of zinc acetate, zinc nitrate or zinc chloride; preferably zinc acetate or anhydrous zinc acetate.

[0030] Preferably, the mass ratio of the zinc salt to hexamethylenetetramine is 0.1-0.4:(0.1-0.5); preferably, the mass ratio of the zinc salt to hexamethylenetetramine is 0.1-0.3:(0.1-0.3).

[0031] Preferably, the water is deionized water.

[0032] Preferably, the ratio of the zinc salt to water is 0.1-0.4 g: (20-100) mL; preferably 0.1-0.3 g: (20-80) mL.

[0033] Preferably, the insulation temperature is 80-100°C, preferably 85-90°C.

[0034] Preferably, the insulation time is 8-12 hours, preferably 10-12 hours.

[0035] A third aspect of the present invention provides an application of a zinc oxide-based electromagnetic wave absorbing material.

[0036] Application of the above zinc oxide-based electromagnetic wave absorbing material in the preparation of electromagnetic wave absorbing equipment.

[0037] An electromagnetic wave absorbing device comprises the above-mentioned zinc oxide-based electromagnetic wave absorbing material.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The zinc oxide-based electromagnetic wave absorbing material of the present invention optimizes the microstructure of the resulting sample by regulating the mass ratio of ZnO and metal ions (e.g., nickel ions and cobalt ions). The resulting core-shell structure product not only optimizes the structure but also improves the impedance matching of the material. The core-shell structure of the zinc oxide-based electromagnetic wave absorbing material increases the heterojunction interface of the material, significantly scattering and reflecting incident electromagnetic waves, thereby improving the material's electromagnetic wave absorption performance.

[0040] (4) The zinc oxide-based electromagnetic wave absorbing material ZnO / NiCo2O4 of the present invention has good electromagnetic wave absorbing performance, and the minimum reflection loss can be less than -55dB, for example, -59.93dB, and the effective absorption bandwidth is 10.96-17.36GHz, that is, the effective absorption bandwidth is 6.40GHz.

[0041] (3) The preparation method of the present invention is simple. During the preparation process, the present invention adopts a simple hydrothermal method and annealing process, and the annealing temperature may not exceed 400° C., which greatly simplifies the preparation process.

[0042] (2) The preparation method of the present invention has low preparation cost and is environmentally friendly and pollution-free. During the preparation process, the present invention does not use organic solvents such as DMF and methanol, but uses deionized water and ethanol as solvents, which reduces costs to a certain extent and does not generate waste liquid harmful to the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is the X-ray diffraction pattern of the rod-shaped ZnO prepared in Example 1;

[0044] Figure 2 This is the SEM image of the rod-shaped ZnO prepared in Example 1;

[0045] Figure 3 This is a graph showing the microwave absorption performance of the rod-shaped ZnO prepared in Example 1;

[0046] Figure 4 The X-ray diffraction pattern of the zinc oxide-based electromagnetic wave absorbing material prepared in Example 1;

[0047] Figure 5 This is an SEM image of the zinc oxide-based electromagnetic wave absorbing material prepared in Example 1;

[0048] Figure 6 This is a graph showing the microwave absorption performance of the zinc oxide-based electromagnetic wave absorbing material prepared in Example 1;

[0049] Figure 7 This is a diagram of the microwave absorption performance of the magnetic NiCo2O4 coated ZnO whisker absorbing material of comparative example 1. DETAILED DESCRIPTION

[0050] In order to make the technical solution of the present invention more clearly understood by those skilled in the art, the following examples are given for illustration. It should be noted that the following examples do not limit the scope of protection claimed by the present invention.

[0051] Unless otherwise specified, the raw materials, reagents, or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0052] Example 1: Preparation of zinc oxide-based electromagnetic wave absorbing material

[0053] A method for preparing a zinc oxide-based electromagnetic wave absorbing material comprises the following steps:

[0054] (1) Preparation of rod-shaped ZnO: 0.2 g of anhydrous zinc acetate and 0.2 g of hexamethylenetetramine were added to 60 mL of deionized water and stirred for 2 h to obtain a mixture. The mixture was transferred to a 100 mL PTFE (polytetrafluoroethylene) liner and maintained at 90 °C for 12 h. The mixture was then cooled to room temperature (25 °C) and washed with deionized water. The product was dried at 60 °C to obtain rod-shaped ZnO.

[0055] (2) Preparation of zinc oxide-based electromagnetic wave absorbing material: 0.1455 g of the rod-shaped ZnO prepared in step (1) was added to 40 mL of deionized water and 20 mL of ethanol and ultrasonically dispersed for 2 h to obtain a mixed solution. Under magnetic stirring, 1 mmol of nickel nitrate hexahydrate, 2 mmol of nickel nitrate hexahydrate and 6 mmol of hexamethylenetetramine were added to the mixed solution and continued to stir for 1 h. The obtained mixture was transferred to a 100 mL PTFE liner and kept at 90 ° C for 10 h. After cooling to room temperature, the product was collected by centrifugation with deionized water and dried at 60 ° C for 12 h. Finally, it was precipitated at 5 ° C·min under N2 atmosphere. -1 The material was annealed at 400°C for 3 hours at a heating rate of 10000 ℃ to obtain a zinc oxide-based electromagnetic wave absorbing material (denoted as ZnO / NiCo2O4).

[0056] Comparative Example 1

[0057] Comparative Example 1 is the magnetic NiCo2O4-coated ZnO whisker absorbing material prepared in Example 1 of CN112897570A.

[0058] Product effect testing

[0059] Figure 1 The X-ray diffraction pattern of the rod-shaped ZnO prepared in Example 1; Figure 1 ( Figure 1 In the figure, "degree" indicates degree, "Intensity" indicates intensity, and "ZnO standard PDF" indicates ZnO standard card), it can be seen that ZnO has diffraction peaks at 31.7°, 34.4°, 36.2°, 47.5°, 56.5°, 62.8°, 66.3°, 67.9° and 69.0°.

[0060] Figure 2 The SEM image of the rod-shaped ZnO prepared in Example 1; Figure 2 It can be seen that ZnO has a rod-like structure with a diameter of about 100 nm and a large aspect ratio (about 10-18:1), which is conducive to the construction of a conductive network.

[0061] Figure 3 This is a graph showing the microwave absorption performance of the rod-shaped ZnO prepared in Example 1; Figure 3 ( Figure 3In (a), “Thickness” indicates thickness, “Frequency” indicates frequency, and “RL” indicates reflection loss. min " represents the minimum reflection loss, Figure 3 In (b), “Thickness” indicates thickness, “Frequency” indicates frequency, and “EAB max " represents the maximum effective absorption bandwidth, d represents the thickness) is the microwave absorption performance diagram of rod-shaped ZnO when the filling amount in paraffin is 40wt%. Figure 3 The following information can be seen: when the filling amount of rod-shaped ZnO in paraffin is 40wt%, the minimum reflection loss RL min =-20.09dB, corresponding to a thickness of 3.1mm; the maximum effective absorption bandwidth is 4.8GHz (13.2-18GHz).

[0062] Figure 4 The X-ray diffraction pattern of the zinc oxide-based electromagnetic wave absorbing material prepared in Example 1; Figure 4 ( Figure 4 (where "degree" indicates degree, "Intensity" indicates intensity, "ZnO standard PDF" indicates ZnO standard card, and "NiCo2O4 standard PDF" indicates NiCo2O4 standard card) It can be seen that 31.7°, 34.4°, 36.2°, 47.5°, 56.5°, 62.8°, 66.3°, 67.9° and 69.0° correspond to the absorption peaks of ZnO, respectively, and 18.8°, 31.0°, 36.9°, 44.2°, 58.9°, 64.5° and 76.6° correspond to the absorption peaks of NiCo2O4, indicating that the zinc oxide-based electromagnetic wave absorption material prepared in Example 1 is composed of ZnO and NiCo2O4.

[0063] Figure 5 This is the SEM image of the zinc oxide-based electromagnetic wave absorbing material prepared in Example 1; Figure 5 It can be seen that NiCo2O4 nanosheets grow uniformly and densely on the surface of the rod-shaped ZnO, which greatly increases the surface area of ​​the material. The ZnO / NiCo2O4 material still maintains a rod-shaped structure with an aspect ratio of approximately 3-7:1.

[0064] Figure 6 This is a graph showing the microwave absorption performance of the zinc oxide-based electromagnetic wave absorbing material prepared in Example 1; Figure 6 ( Figure 6 In (a), “Thickness” indicates thickness, “Frequency” indicates frequency, and “RL” indicates reflection loss. min " represents the minimum reflection loss, Figure 6In (b), “Thickness” indicates thickness, “Frequency” indicates frequency, and “EAB max " represents the maximum effective absorption bandwidth, d represents the thickness) is the microwave absorption performance diagram of rod-shaped ZnO when the filling amount in paraffin is 40wt%. Figure 6 It can be seen that when the filling amount of zinc oxide-based electromagnetic wave absorbing material in paraffin is 40wt%, the minimum reflection loss RL min =-59.93dB, corresponding to a thickness of 2.6mm; the maximum effective absorption bandwidth is 6.4GHz (10.96-17.36GHz).

[0065] Figure 7 The microwave absorption performance diagram of the magnetic NiCo2O4 coated ZnO whisker absorbing material of comparative example 1 is shown in FIG. In the magnetic NiCo2O4 coated ZnO whisker absorbing material of comparative example 1, most of the ZnO rods are covered by seaweed-like NiCo2O4, and the aspect ratio of the material is about 8-15:1. Figure 7 ( Figure 7 In (a), “Thickness” indicates thickness, “Frequency” indicates frequency, and “RL” indicates reflection loss. min " represents the minimum reflection loss, Figure 7 In (b), “Thickness” indicates thickness, “Frequency” indicates frequency, and “EAB max ” represents the maximum effective absorption bandwidth, and d represents the thickness). It can be seen that when the filling amount of the magnetic NiCo2O4 coated ZnO whisker absorber in paraffin is 40wt%, the minimum reflection loss RL min =-56.17dB, corresponding to a thickness of 3.5mm; the effective absorption bandwidth is 4.32GHz (9.36-13.68GHz).

[0066] The present invention prepares rod-shaped ZnO / NiCo2O4 materials by uniformly and densely growing NiCo2O4 nanosheets on ZnO nanorods. The zinc oxide-based electromagnetic wave absorbing material with a high specific surface area leads to a large amount of incident waves, rather than unfavorable reflections on the surface. NiCo2O4 nanosheets cause multiple reflections and scattering of the incident waves, which promotes the attenuation of electromagnetic waves. Secondly, zinc oxide-based electromagnetic wave absorbing materials with a suitable aspect ratio (approximately 1:3 to 1:7) easily form a 3D conductive network, and the core-shell structure also forms a local microcurrent network. This causes the internal electrons to migrate in a directional manner under an external magnetic field, thereby converting electromagnetic energy into thermal energy. In addition, the zinc oxide-based electromagnetic wave absorbing material provides a large number of heterogeneous interfaces, which leads to a large amount of space charge accumulation, thereby increasing the interface polarization. Therefore, the core-shell ZnO / NiCo2O4 material has excellent electromagnetic wave absorption performance: when the filling amount of the material is 40wt%, the minimum reflection loss is increased from -20.09 to -59.93dB; the effective absorption bandwidth is increased from 4.8 to 6.4GHz, which is a huge improvement compared to rod-shaped ZnO.

[0067] The superior performance of the zinc oxide-based electromagnetic wave absorbing material of the present invention primarily stems from the improved impedance matching achieved by its core-shell structure, which significantly facilitates the penetration of electromagnetic waves into the material. Furthermore, the numerous heterojunction interfaces and conductive networks provided by the core-shell structure significantly enhance dielectric loss capability. In summary, the combined effects of these multiple electromagnetic wave loss mechanisms ensure the strong absorption of incident electromagnetic waves by the zinc oxide-based electromagnetic wave absorbing material of the present invention.

[0068] In addition, within the scope of the present invention, by changing the relationship between the amounts of the raw materials, for example, by adjusting the mass ratio of rod-shaped ZnO, nickel salt, cobalt salt and hexamethylenetetramine within the range of (0.1-3): (0.2-4): (0.3-6): 3.1, or by changing the process parameters, the obtained product effect is similar to that of Example 1.

Claims

1. A zinc oxide-based electromagnetic wave absorbing material, characterized in that: The zinc oxide-based electromagnetic wave absorbing material has core-shell morphology and rod-like structure. The core is composed of ZnO, and the shell is composed of NiCo2O4. The NiCo2O4 is in the form of nanosheets. The zinc oxide-based electromagnetic wave absorbing material has an aspect ratio of 1:(2-7); The preparation method of the zinc oxide-based electromagnetic wave absorbing material comprises the following steps: Rod-shaped ZnO is dispersed in a mixed solution of deionized water and alcohol, ultrasonically dispersed, and then nickel salt, cobalt salt and hexamethylenetetramine are added. The mixture is kept warm, cooled, and separated to obtain the precursor ZnO / NiCo(OH) x , the X is greater than 0; The precursor ZnO / NiCo(OH) x Annealing treatment is performed to obtain the zinc oxide-based electromagnetic wave absorbing material.

2. The zinc oxide-based electromagnetic wave absorbing material according to claim 1, characterized in that: The zinc oxide-based electromagnetic wave absorbing material has a length of 1-5 μm and a diameter of 100-600 nm.

3. The zinc oxide-based electromagnetic wave absorbing material according to claim 1, characterized in that The effective absorption bandwidth of the zinc oxide-based electromagnetic wave absorbing material is 10.96-17.36 GHz.

4. The zinc oxide-based electromagnetic wave absorbing material according to claim 1, characterized in that: The minimum reflection loss of the zinc oxide-based electromagnetic wave absorbing material is less than -55dB.

5. The zinc oxide-based electromagnetic wave absorbing material according to claim 1, characterized in that: The nickel salt is selected from at least one of nickel nitrate, nickel chloride or nickel sulfate; the cobalt salt is selected from at least one of cobalt nitrate, cobalt chloride or cobalt sulfate.

6. The zinc oxide-based electromagnetic wave absorbing material according to claim 1, characterized in that: The mass ratio of the rod-shaped ZnO, nickel salt, cobalt salt and hexamethylenetetramine is (0.1-3): (0.2-4): (0.3-6): 3.

1.

7. The zinc oxide-based electromagnetic wave absorbing material according to claim 1, characterized in that: The annealing treatment is carried out under the protection of inert gas; the heating rate during the annealing treatment is 1-30℃·min -1 ; The temperature during the annealing process is raised to 300-1000°C; the annealing time is 1-15h.

8. An electromagnetic wave absorbing device, characterized in that: The invention comprises the zinc oxide-based electromagnetic wave absorbing material according to any one of claims 1 to 7.

Images