Flower-like ZnO-hard carbon composite material, preparation method and application thereof

Abstract

The application discloses a kind of flower-shaped ZnO-hard carbon composite materials and preparation method and application thereof, comprising the following steps: (1) under stirring condition, Zn metal organic complex solution is dropped or injected into phenolic resin solution, after droping is completed, continue stirring, then NaHCO3 solution is added, to obtain precursor mixed solution;(2) the precursor mixed solution is heated and stirred to solidify;(3) the solidified precursor is heated to the first temperature under inert atmosphere protection and annealed, then heated to the second temperature and carbonized.The three-dimensional flower-shaped structure of ZnO nanoparticles self-assembled in the composite material is uniformly dispersed in hard carbon matrix, this multi-level heterogeneous interface not only enhances the interface polarization effect, but also effectively attenuates electromagnetic wave energy through multiple scattering and reflection mechanism, realizes excellent electromagnetic wave absorption characteristics.

Description

Technical Field

[0001] This invention belongs to the field of microwave absorbing materials, and particularly relates to a flower-shaped ZnO-hard carbon composite material, its preparation method and application. Background Technology

[0002] The research and development of microwave absorbing materials has always been closely linked to the needs of national defense security and civilian technology development. In the civilian sector, with the rapid popularization of 5G communication and Internet of Things technologies, the complexity of the electromagnetic environment has significantly increased, and traditional microwave absorbing materials can no longer meet the growing electromagnetic compatibility requirements. At the same time, the trend of thinner and lighter electronic devices has placed more stringent requirements on the thickness and weight of microwave absorbing materials. These application needs are driving the development of microwave absorbing materials towards ultra-thin, wide-bandwidth, and intelligent response, giving rise to a research and development boom of next-generation high-performance microwave absorbing materials.

[0003] Traditional microwave absorbing materials, such as ferrites and carbon-based materials, often suffer from inherent drawbacks in practical applications, such as high density, narrow bandwidth, or insufficient environmental stability. In recent years, composite systems of metal oxides and carbon materials have shown unique advantages due to their tunable electromagnetic parameters and good stability. Among them, zinc oxide (ZnO) has attracted much attention due to its special semiconductor properties and rich morphological tunability; however, single ZnO materials suffer from limited dielectric loss and poor impedance matching. Hard carbon materials, with their abundant structural defects and stable chemical properties, can effectively enhance dielectric loss. However, achieving optimized composites of ZnO and hard carbon to present novel nanostructures for high-performance microwave absorption remains a significant technical challenge. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a flower-like ZnO-hard carbon composite material, its preparation method and application, to improve the microwave absorption performance.

[0005] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0006] A method for preparing a flower-like ZnO-hard carbon composite material includes the following steps:

[0007] (1) Under stirring conditions, the Zn organometallic complex solution is added dropwise or injected into the phenolic resin solution. After the addition is completed, stirring is continued, and then NaHCO3 solution is added to obtain a precursor mixed solution.

[0008] The rate at which the Zn organometallic complex solution is dropped or injected into the phenolic resin solution is m / 2000-m / 1000 g / min, where m is the mass of the phenolic resin solution in grams.

[0009] The mass ratio of the Zn organometallic complex solution, the phenolic resin solution, and the NaHCO3 solution is (5-10):(5-10):1;

[0010] (2) Heat and stir the precursor mixture solution to solidify it;

[0011] (3) The cured precursor is annealed at a first temperature under an inert atmosphere and then carbonized at a second temperature to obtain flower-shaped ZnO-hard carbon composite material.

[0012] As a further improvement, the Zn organometallic complex solution in step (1) is anhydrous ethanol or acetone solution; the phenolic resin is anhydrous ethanol or acetone solution; and the NaHCO3 solution is an aqueous solution.

[0013] As a further improvement, the organometallic complex of Zn in step (1) is one of zinc acetylacetonate, zinc stearate or zinc acetate.

[0014] As a further improvement, the concentration of the Zn organometallic complex solution in step (1) is 0.5-1.5 mol / L; the concentration of the phenolic resin solution is 400-600 g / L; and the concentration of the NaHCO3 solution is 0.05-0.15 mol / L.

[0015] As a further improvement, the stirring rate in step (1) is 100-200 r / min.

[0016] As a further improvement, the heating temperature in step (2) is 40-60℃, and the stirring rate during heating is 100-200 r / min.

[0017] As a further improvement, in step (3), the first temperature is 90-110℃ and the second temperature is 600-1200℃.

[0018] As a further improvement, step (3) involves holding the temperature at the first temperature for 0.8-1.2 hours and at the second temperature for 2-4 hours.

[0019] The present invention provides a flower-like ZnO-hard carbon composite material, which is prepared by the preparation method described above, wherein ZnO exists in the form of particles or flakes and forms a flower-like micro-nano structure through self-assembly and is uniformly distributed in the hard carbon matrix.

[0020] The present invention also provides an application of the flower-like ZnO-hard carbon composite material in microwave absorption.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] In terms of material properties, this composite material achieves excellent electromagnetic wave absorption characteristics through a unique flower-like structure design. The three-dimensional flower-like structure formed by the self-assembly of ZnO nanoparticles is uniformly dispersed within a hard carbon matrix. This multi-level heterogeneous interface not only enhances the interfacial polarization effect but also effectively attenuates electromagnetic wave energy through multiple scattering and reflection mechanisms. The material exhibits broadband and efficient wave absorption performance, and is expected to meet the performance requirements of modern stealth technology and electromagnetic shielding materials.

[0023] In terms of preparation process, the solvothermal-carbonization synergistic preparation method adopted in this invention has significant technical advantages. This method enables one-step synthesis of flower-like ZnO-hard carbon composite materials by precisely controlling the precursor ratio and heat treatment process. The entire process is simple and controllable, with mild reaction conditions, exhibiting excellent batch stability and reproducibility. Compared with traditional mechanical mixing methods, this preparation method significantly improves production efficiency and raw material utilization, providing a reliable technical path for large-scale industrial production. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a SEM image of a flower-like ZnO-hard carbon composite material;

[0026] Figure 2 This is a high-magnification SEM image of a flower-shaped ZnO-hard carbon composite material.

[0027] Figure 3 The XRD pattern of the flower-like ZnO-hard carbon composite material is shown.

[0028] Figures 4-5 These are the three-dimensional and two-dimensional reflection loss spectra of ZC-700 (Example 1);

[0029] Figures 6-7 These are the three-dimensional and two-dimensional reflection loss spectra of ZC-900 (Example 2);

[0030] Figures 8-9 These are the three-dimensional and two-dimensional reflection loss spectra of ZC-1100 (Example 2);

[0031] Figure 10 This is a SEM image of the comparison scale 1.

[0032] Figure 11This is the SEM image of the comparison image 2. Detailed Implementation

[0033] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0034] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0035] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0036] In some specific embodiments, the preparation method of the flower-like ZnO-hard carbon composite material of the present invention includes the following steps:

[0037] (1) Under stirring conditions, the Zn organometallic complex solution is added dropwise or injected into the phenolic resin solution. After the addition is completed, stirring is continued, and then NaHCO3 solution is added to obtain a precursor mixed solution.

[0038] First, three precursor solutions need to be prepared: a Zn organometallic complex solution, a phenolic resin solution, and a NaHCO3 solution.

[0039] In some embodiments, a Zn organometallic complex is dissolved in anhydrous ethanol or acetone to form a Zn organometallic complex solution. The Zn organometallic complex is zinc acetylacetonate (Zn(acac)2) or zinc stearate (Zn(C... 17 H 35 One of zinc acetylacetonate (Zn(CH3COO)2) or zinc acetate (Zn(CH3COO)2). Zinc acetylacetonate (Zn(acac)2) is preferred because it has low industrial production costs and is more soluble in phenolic resins. The concentration of the organometallic complex solution of Zn is 0.5-1.5 mol / L, preferably 1.2 mol / L.

[0040] In some embodiments, phenolic resin is diluted in anhydrous ethanol or acetone to form a phenolic resin solution. The concentration of the phenolic resin solution is 400-600 g / L, preferably 500 g / L.

[0041] In some embodiments, NaHCO3 powder is dissolved in deionized water to form a NaHCO3 solution. The concentration of the NaHCO3 solution is 0.05-0.15 mol / L, preferably 0.1 mol / L.

[0042] In some embodiments, the mass ratio of the Zn organometallic complex solution, the phenolic resin solution, and the NaHCO3 solution is (5-10):(5-10):1, preferably 8:8:1.

[0043] In some embodiments, the stirring rate under the stirring conditions is 100-200 r / min, preferably 150 r / min.

[0044] In some embodiments, the rate at which the Zn organometallic complex solution is dropped or injected into the phenolic resin solution is (m / 2000-m / 1000) g / min, where m is the mass (grams) of the phenolic resin solution, preferably m / 1000 g / min.

[0045] In some embodiments, stirring continues for 2-2.5 hours after the addition is complete.

[0046] The Zn organometallic complex solution needs to be slowly injected into the phenolic resin solution at a precisely controlled rate (preferably 0.01 g / min). During the entire injection process, the mixture is stirred at the above-mentioned stirring speed. After a period of time following the completion of the injection, NaHCO3 solution is added to form a stable precursor (ZN-PR) mixed solution.

[0047] (2) Heat and stir the precursor mixture solution to solidify it.

[0048] In some embodiments, the heating temperature is 40-60°C, preferably 50°C.

[0049] In some embodiments, the stirring rate during heating is 100-200 r / min, preferably 200 r / min, and rapid stirring can avoid segregation.

[0050] In some embodiments, the mixture is heated and stirred for 5-7 hours to allow it to gradually solidify.

[0051] To remove moisture and volatile ethanol from the precursor, the mixed solution is solidified while being stirred on a heating platform at 40-60°C to prevent component segregation.

[0052] (3) The cured precursor is annealed at a first temperature under an inert atmosphere and then carbonized at a second temperature to obtain flower-shaped ZnO-hard carbon composite material.

[0053] In some embodiments, the inert gas is nitrogen or argon.

[0054] In some embodiments, the first temperature is 90-110°C, preferably 100°C. The temperature is increased to the first temperature at a rate of 8-12°C / min and held for 0.8-1.2 hours. The second temperature is 600-1200°C, preferably 700°C. The temperature is increased to the second temperature at a rate of 8-12°C / min and held for 2-4 hours.

[0055] The cured precursor was then subjected to step heat treatment under an inert atmosphere. First, it was annealed at low temperature to completely remove moisture and residual solvent and to thoroughly cure ZN-PR. Then, it was annealed at high temperature to carbonize the organic solvent. Finally, it was washed with deionized water to obtain flower-shaped ZnO-hard carbon composite material.

[0056] The flower-like ZnO-hard carbon composite material prepared by this method possesses a unique microstructure and excellent properties. ZnO is uniformly dispersed in the hard carbon matrix in a flower-like structure, forming a good interfacial bond. This hierarchical structure endows the material with excellent electromagnetic wave absorption properties. The entire preparation process has precise and controllable parameters, good repeatability, and is suitable for large-scale production. This method achieves precise control over the microstructure of the material by optimizing the precursor ratio, mixing process, and heat treatment conditions.

[0057] The main process for preparing flower-like ZnO-hard carbon composite materials according to this invention is as follows:

[0058] First, the Zn(acac)2 in the cured ZN-PR decomposes at high temperature, as shown in the following equation.

[0059] Zn(acac)2(g) → Zn(acac)·(g) + (acac)(g)

[0060] Zn(acac)·(g) → Zn(g) + (acac)·(g)

[0061] The generated zinc atoms are surrounded by phenolic resin, making it difficult for them to escape from the surface for further reaction. Simultaneously, the gaseous (acac) further decomposes, providing a large number of carbon atoms and oxygen-containing gases, including H2O, CO2, and CH2OH, resulting in numerous pores within the ZN-PR structure. Furthermore, the introduced NaHCO3 increases additional pore channels, facilitating the diffusion of Zn atoms and promoting the formation of flower-like zinc oxide. Due to the high chemical reactivity of zinc atoms, they react with these oxygen-containing gases to form ZnO molecules.

[0062] Second, ZnO molecules migrate within the pores of ZN-PR, gradually forming aggregates, and eventually forming flower-like ZnO clusters.

[0063] Third, phenolic resin undergoes carbonization at high temperatures, eventually coating flower-shaped ZnO clusters to obtain flower-shaped ZnO-hard carbon composite material.

[0064] To form flower-like ZnO-hard carbon composite materials with special morphology, the following conditions need to be strictly controlled:

[0065] (a) The rate at which the organometallic complex solution of Zn is injected into the phenolic resin solution in step (1);

[0066] (b) Heating and curing temperature and stirring rate in step (2);

[0067] (c) The ratio of the organometallic complex (zinc acetylacetonate) solution and the phenolic resin solution of Zn;

[0068] (d) Carbonization temperature in step (3).

[0069] First, the slow injection and stirring technique in (a) and the low-temperature stirring and curing technique in (b) are crucial for ensuring the uniform dispersion of zinc acetylacetonate in phenolic resin. Viscous phenolic resin easily causes zinc acetylacetonate to agglomerate, reducing the uniformity of the flower-like ZnO distribution. Second, the ratio of zinc acetylacetonate to phenolic resin is critical. Too low a ratio results in insufficient raw materials for flower-like ZnO formation, while too high a ratio leads to significant agglomeration. Finally, the carbonization temperature is important. Too high a temperature causes zinc acetylacetonate to decompose too quickly, leading to rapid diffusion of Zn atoms and even overflow from the phenolic resin. Too low a temperature results in incomplete decomposition and incomplete carbonization of the phenolic resin, making it difficult to form a hard carbon structure. In summary, all of the above conditions are crucial for forming flower-like ZnO-hard carbon composite materials, and each condition plays a role in promoting the formation of the material structure.

[0070] The present invention relates to a flower-like ZnO-hard carbon composite material, wherein ZnO exists in the form of particles or flakes and forms flower-like micro / nano structures through self-assembly, which are uniformly distributed in a hard carbon matrix. These three-dimensional flower-like structures are uniformly distributed in the hard carbon matrix, forming a composite system resembling a profusion of flowers, thus achieving uniform microscale composite of ZnO and hard carbon.

[0071] The flower-shaped ZnO-hard carbon composite material of the present invention is suitable for microwave absorption and has wide bandwidth and high loss microwave absorption performance.

[0072] The flower-like ZnO-hard carbon composite material of this invention constructs a flower-like structure with multi-level scattering characteristics by precisely controlling the microstructure of ZnO. Simultaneously, a uniform hard carbon coating layer optimizes impedance matching and enhances the interfacial polarization effect. This unique structural design not only significantly improves the material's dielectric loss capability but also achieves efficient absorption and dissipation of electromagnetic waves. Compared to traditional composite materials, this material exhibits significant advantages in absorption intensity, operating bandwidth, and environmental stability, providing an important technical path for the development of next-generation high-performance microwave absorbing materials and showing broad application prospects in military stealth and civilian electromagnetic protection fields.

[0073] Example 1

[0074] First, prepare the three precursor solutions required for the experiment. Dissolve zinc acetylacetonate in anhydrous ethanol and sonicate for 30 minutes to fully dissolve it to form a 1.2 mol / L zinc precursor solution. Prepare a 0.1 mol / L NaHCO3 aqueous solution. Dilute phenolic resin in acetone to form a 500 g / L solution.

[0075] 10.0 g of phenolic resin solution was placed in a reaction vessel. A zinc precursor solution was slowly added dropwise at a rate of 0.01 g / min while stirring at 150 r / min. After the addition was complete, stirring was continued for 2 hours. Subsequently, 5 mL of NaHCO3 solution was added to form a stable ZN-PR mixed solution. The mass ratio of the Zn organometallic complex solution, the phenolic resin solution, and the NaHCO3 solution was 8:8:1.

[0076] The Zn-PR mixture was placed on a heating platform and solidified at 50°C with stirring (200 r / min) for 6 hours to remove volatiles. Then, it was placed in a vacuum tube furnace and subjected to step heat treatment under nitrogen protection: first, the temperature was increased to 100°C at 10°C / min and held for 1 hour; then, the temperature was increased to 700°C at 10°C / min and carbonized for 3 hours. After washing three times with deionized water, the flower-like ZnO-hard carbon composite material ZC-700 was finally obtained.

[0077] Example 2

[0078] Parallel experiments were conducted according to Example 1. In one set of parallel experiments, only the reaction temperature was changed to 900°C, while other conditions remained unchanged, as detailed below:

[0079] Zinc acetylacetone was dissolved in anhydrous ethanol and sonicated for 30 minutes to fully dissolve it, forming a 1.2 mol / L zinc precursor solution; a 0.1 mol / L NaHCO3 aqueous solution was prepared; and phenolic resin was diluted in acetone to form a 500 g / L solution.

[0080] 10.0 g of phenolic resin solution was placed in a reaction vessel. A zinc precursor solution was slowly added dropwise at a rate of 0.01 g / min while stirring at 150 r / min. After the addition was complete, stirring was continued for 2 hours. Subsequently, 5 mL of NaHCO3 solution was added to form a stable ZN-PR mixed solution. The mass ratio of the Zn organometallic complex solution, the phenolic resin solution, and the NaHCO3 solution was 8:8:1.

[0081] The ZN-PR mixed solution was placed on a heating platform and solidified at 50°C with stirring (200 r / min) for 6 hours to remove volatiles. Then, it was placed in a vacuum tube furnace and subjected to step heat treatment under nitrogen protection: first, the temperature was increased to 100°C at 10°C / min and held for 1 hour, then increased to 900°C at 10°C / min and carbonized for 3 hours. After the reaction was complete, the solution was washed three times with deionized water, and the collected product was labeled ZC-900.

[0082] In another set of parallel experiments, the reaction temperature was set to 1100℃, and the above experimental process was repeated. The corresponding collected products were labeled ZC-1100.

[0083] Figure 1 This is a SEM image of a flower-like ZnO-hard carbon composite material (ZC-700); the white dots are ZnO flower-like structures, evenly distributed in the hard carbon, presenting a flower-like structure.

[0084] Figure 2 This is a high-magnification SEM image of the flower-shaped ZnO-hard carbon composite material (ZC-700), clearly showing white ZnO particles;

[0085] Figure 3 The XRD pattern is shown in the image.

[0086] Figures 4-5 The three-dimensional and two-dimensional reflection loss spectra of the ZC-700 (Example 1) are shown respectively; the optimal reflection loss value is -54.4 dB and the maximum effective bandwidth is 5.8 GHz.

[0087] Figures 6-7 The three-dimensional and two-dimensional reflection loss spectra of the ZC-900 (Example 2) are shown respectively; the optimal reflection loss value is -39.3 dB, and the maximum effective bandwidth is 7.1 GHz.

[0088] Figures 8-9 The three-dimensional and two-dimensional reflection loss spectra of ZC-1100 (Example 2) are shown respectively; the optimal reflection loss value is -40 dB and the maximum effective bandwidth is 7.7 GHz.

[0089] Comparative Example 1

[0090] Compared with Example 1, the difference is that the slow injection stirring technique and the low-temperature stirring curing technique are not used, that is:

[0091] The phenolic resin solution and zinc precursor solution were directly mixed instead of being injected slowly at a rate of 0.01 g / min.

[0092] During the curing stage at 50°C, no continuous stirring was performed; the material was allowed to cure naturally.

[0093] The products formed, such as Figure 10 As shown, the white ZnO exhibits severe agglomeration, with blank ZnO areas appearing in the hard carbon region, forming numerous black aggregated areas. Its optimal reflection loss is less than -10dB, and its effective bandwidth is 0.

[0094] Comparative Example 2

[0095] Compared with Example 1, the difference is that a high proportion of Zn organometallic complex solution is used, that is, the proportion of Zn organometallic complex solution is increased to twice that of Example 1, and the mass ratio of Zn organometallic complex solution, phenolic resin solution and NaHCO3 solution is 16:8:1.

[0096] The products formed, such as Figure 11 As shown, the white ZnO agglomeration phenomenon is also severe, with the ZnO blank areas tightly connected to form a dense distribution, and no flower-like structure was observed. Its optimal reflection loss is less than -10dB, and its effective bandwidth is 0.

[0097] This invention employs a slow-injection stirring technique and a low-temperature stirring and curing technique to uniformly mix a Zn organometallic complex solution with a phenolic resin solution, and introduces NaHCO3 to increase porosity and provide channels for zinc atom diffusion. No additional curing agent is required. After heating and stirring for curing, the mixture undergoes high-temperature annealing under an inert atmosphere, ultimately yielding a ZnO-hard carbon composite material with a flower-like micro / nano structure. In this composite material, ZnO self-assembles in particle or plate form to form a three-dimensional flower-like structure, uniformly dispersed within a hard carbon matrix, exhibiting excellent broadband microwave absorption performance and achieving highly efficient electromagnetic wave attenuation. This invention provides a new approach to the structural design and fabrication of high-performance microwave absorbing materials, and has significant application value in advanced stealth technology and electromagnetic protection.

[0098] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims

1. A method for preparing a flower-like ZnO-hard carbon composite material, characterized in that, Includes the following steps: (1) Under stirring conditions, the Zn organometallic complex solution is added dropwise or injected into the phenolic resin solution. After the addition is completed, stirring is continued, and then NaHCO3 solution is added to obtain a precursor mixed solution. The organometallic complex of Zn is one of zinc acetylacetonate, zinc stearate, or zinc acetate. The rate at which the Zn organometallic complex solution is dropped or injected into the phenolic resin solution is m / 2000-m / 1000 g / min, where m is the mass of the phenolic resin solution in grams. The mass ratio of the Zn organometallic complex solution, the phenolic resin solution, and the NaHCO3 solution is (5-10):(5-10):1; (2) The precursor mixture solution is heated and stirred to solidify it; the heating temperature is 40-60℃ and the stirring rate during heating is 100-200 r / min; (3) The cured precursor is annealed at a first temperature under an inert atmosphere and then carbonized at a second temperature to obtain flower-shaped ZnO-hard carbon composite material; the first temperature is 90-110℃ and the second temperature is 600-1200℃.

2. The method for preparing the flower-like ZnO-hard carbon composite material according to claim 1, characterized in that, In step (1), the Zn organometallic complex solution is anhydrous ethanol or acetone solution; the phenolic resin is anhydrous ethanol or acetone solution; and the NaHCO3 solution is an aqueous solution.

3. The method for preparing the flower-like ZnO-hard carbon composite material according to claim 1, characterized in that, In step (1), the concentration of the Zn organometallic complex solution is 0.5-1.5 mol / L; the concentration of the phenolic resin solution is 400-600 g / L; and the concentration of the NaHCO3 solution is 0.05-0.15 mol / L.

4. The method for preparing the flower-like ZnO-hard carbon composite material according to claim 1, characterized in that, The stirring rate in step (1) is 100-200 r / min.

5. The method for preparing the flower-like ZnO-hard carbon composite material according to claim 1, characterized in that, Step (3) Keep warm at the first temperature for 0.8-1.2 hours and at the second temperature for 2-4 hours.

6. A flower-like ZnO-hard carbon composite material, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 5, wherein ZnO exists in the form of particles or flakes and forms a flower-like micro-nano structure through self-assembly and is uniformly distributed in a hard carbon matrix.

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