Fe / Co / Ni nanoparticle loaded N, O-doped walnut-like porous carbon composite microspheres and a preparation method thereof

Abstract

The present application relates to a kind of Fe / Co / Ni nanoparticle loaded N, O doped walnut-like porous carbon composite microspheres and its preparation method, the preparation method includes the synthesis of polymer microsphere base, the synthesis of polymer microsphere sugar-Fe / Co / Ni composite microspheres and carbonization and the like steps.Under the conditions that the mass ratio of the walnut-like porous carbon composite microspheres and paraffin is 1:4~8 and the matching thickness is 2.0~3.0mm, its minimum reflection loss is-28.5~-48.1dB, and the optimal effective absorption bandwidth is 5.44GHz, so the present application opens a new path for component adjustment, introduces defect engineering and morphology design, and realizes a new preparation method of carbon composite microsphere absorber with excellent electromagnetic wave absorption performance.

Description

Technical field

[0001] The present invention belongs to the technical field of electromagnetic wave absorbing materials. More specifically, the present invention relates to N,O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles, and also to a method for preparing the N,O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles. [Background Technology]

[0002] With the rapid development of wireless communication technology and the widespread use of sophisticated electronic devices, the indispensable role of electromagnetic waves has become increasingly prominent. While electromagnetic waves bring great convenience to people, they also generate significant electromagnetic radiation and pollution, impacting their health. Furthermore, electromagnetic waves pose a serious threat to military security. Consequently, numerous researchers have focused on developing electromagnetic wave absorbing materials that can attenuate and absorb electromagnetic radiation. High-performance electromagnetic wave absorbing materials should possess strong absorption properties, a wide absorption bandwidth, thin thickness, and light weight. Carbon-based materials, including biomass carbon, carbon microspheres, carbon nanotubes, carbon aerogels, and graphitic carbon, have been explored as dielectric absorbers due to their excellent conductivity, high stability, tunable specific surface area, and lightweight properties. Among these, carbon microspheres have been extensively studied due to their advantages such as good structural controllability and tunable morphology. However, their poor impedance matching and single-loss mechanism impair their electromagnetic wave absorption performance.

[0003] Magnetic materials (such as Fe / Co / Ni metals, metal oxides, and ferrites) have high saturation magnetization, excellent magnetic permeability, and strong absorption properties, making them ideal candidates for electromagnetic wave absorption. Combining magnetic loss materials with carbon microspheres is an effective strategy for enriching the loss mechanism of carbon microspheres and improving impedance matching. The heterogeneous interface between the magnetic and carbon components induces dipole planning and interfacial polarization, while the complementarity between the dielectric and magnetic components can synergistically optimize impedance matching. For example, MY Liu et al., titled "Heating induced self-assemble pomegranate-like Fe3C@Graphite magnetic microspheres on amorphous carbon for high-performance microwave absorption," Composites Part B, 2023, 260: 110767, reported that pomegranate-like Fe3C@graphite core-shell nanoparticles were uniformly embedded in amorphous carbon through a pre-oxidation, impregnation, and heating-induced self-assembly strategy. This unique structure optimizes impedance matching while enhancing interfacial polarization loss and magnetic loss.

[0004] Nanostructure design is an effective approach to optimizing microwave absorption performance. The introduction of bubbles in hollow porous structures can alter the dielectric constant of the material, optimizing impedance matching and allowing more electromagnetic waves to enter the material. Furthermore, the large number of hollow porous structures increases the contact area between air and the material, helping to induce more interfacial polarization. For example, C. Yan et al., in "The efficient absorption of electromagnetic waves by tunable N-doped multi-cavity mesoporous carbon microspheres," Carbon, 2023, 201: 1115–1125, reported using acetone to selectively etch phenolic resin oligomers to induce multi-cavity pores, resulting in unique multi-cavity mesoporous carbon microspheres. Their microwave absorption performance was demonstrated with a minimum reflection loss of -44.5 dB at 1.6 mm and an effective absorption bandwidth of 4.72 GHz. Furthermore, the surface micromorphology of the carbon microspheres also influences their performance. Compared to smooth surfaces, complex and diverse surfaces not only have a larger surface area but also produce multi-directional reflections, facilitating multiple reflections of electromagnetic waves and reducing interfacial polarization losses.

[0005] Although researchers have prepared absorbing composite materials from the above aspects, there is still a need to develop more convenient, green and environmentally friendly preparation strategies to mass-produce multi-morphological absorbing materials with both magnetic loss and dielectric loss.

[0006] In response to the problems of the prior art, the inventors have finally completed the present invention based on summarizing the prior art, through a large amount of experimental research and analysis and summary. [Summary of the invention]

[0007] [Technical problems to be solved]

[0008] The present invention aims to provide N, O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles.

[0009] Another object of the present invention is to provide a method for preparing the N, O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles.

[0010] [Technical solution]

[0011] The present invention is achieved through the following technical solutions.

[0012] The invention relates to a method for preparing N,O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles.

[0013] The preparation steps of the preparation method are as follows:

[0014] A. Synthesis of polymer microsphere substrate

[0015] In a reaction vessel, acrylonitrile, triallyl isocyanurate, and methyl methacrylate are uniformly mixed in a weight ratio of 35-85:5-30:0-5 to obtain a monomer mixture, and then 0.79-1.54% of an initiator and 417-1530% of a pure water solvent, based on the weight of the monomer mixture, are added and stirred uniformly. The mixture is then reacted at a temperature of 70-75° C. and a stirring speed of 600-1000 rpm for 3-6 hours, filtered, and the obtained solid is successively washed with ethanol and deionized water, and then dried in an oven at a temperature of 40-60° C. for 12-24 hours to obtain the polymer microsphere substrate.

[0016] B. Synthesis of polymer microspheres@sugar-Fe / Co / Ni composite microspheres

[0017] 1-5 parts by weight of the polymer microsphere base obtained in step A, 1-10 parts by weight of sugar, and 0.1-0.3 parts by weight of a metal salt are added to 50-60 parts by weight of pure water, and ultrasonic dispersion is performed using an ultrasonic device for 20-30 minutes. The mixture is then reacted in a reactor at a temperature of 180-200° C. for 8-12 hours, filtered, and the obtained solid is washed successively with ethanol and deionized water. The washed solid is dried in an oven at a temperature of 40-60° C. for 12-24 hours, thereby obtaining the polymer microsphere@sugar-Fe / Co / Ni composite microspheres;

[0018] C. Carbonization

[0019] The polymer microspheres@sugar-Fe / Co / Ni composite microspheres obtained in step B are placed in an alumina crucible, and heated from room temperature to 700-900°C at a heating rate of 1.0-3.0°C / min in a tube furnace in an inert protective gas of nitrogen or argon, maintained at this temperature for 1.8-2.2 hours, and then naturally cooled to room temperature, thereby obtaining N,O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles.

[0020] According to a preferred embodiment of the present invention, in step A, the methyl methacrylate can be replaced by one or more monomers selected from styrene, divinylbenzene, ethylene glycol dimethacrylate, diallyl maleate or cyclotrimethylolpropane formal acrylate.

[0021] According to another preferred embodiment of the present invention, in step A, the initiator is one or more initiators selected from azobisisobutylamidine hydrochloride, potassium persulfate, ammonium persulfate or sodium persulfate.

[0022] According to another preferred embodiment of the present invention, in step A, the polymer microspheres are monodisperse polymer microspheres with a particle size of 300 to 600 nm.

[0023] According to another preferred embodiment of the present invention, in step B, the sugar is one or more sugars selected from polydextrose, glucose, D-xylose, xylooligosaccharides, sucrose, lactose, fructooligosaccharides or trehalose.

[0024] According to another preferred embodiment of the present invention, in step B, the metal salt is one or more metal salts selected from cobalt acetate tetrahydrate, nickel acetate tetrahydrate, ferric chloride hexahydrate or cobalt chloride hexahydrate.

[0025] According to another preferred embodiment of the present invention, in step B, the particle size of the polymer microspheres@sugar-Fe / Co / Ni composite microspheres is 300-700 nm.

[0026] The present invention also relates to N, O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles prepared by the preparation method.

[0027] According to a preferred embodiment of the present invention, the N, O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles are carbon microspheres with a diameter of 20 to 90 nm randomly embedded on the surface of the concave-convex carbon microspheres, and micropores and mesopores with an average pore size of 3 to 9 nm are distributed inside the carbon microspheres. Its diameter is 290 to 380 nm, and its specific surface area is 180 to 400 m 2 g -1 .

[0028] According to another preferred embodiment of the present invention, under the conditions of a weight ratio of the walnut-shaped porous carbon composite microspheres to paraffin of 1:4 to 8 and a matching thickness of 2.0 to 3.0 mm, its minimum reflection loss is -28.5 to -48.1 dB, and the optimal effective absorption bandwidth is 5.44 GHz.

[0029] The present invention will be described in more detail below.

[0030] The invention relates to a method for preparing N,O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles.

[0031] The preparation steps of the preparation method are as follows:

[0032] A. Synthesis of polymer microsphere substrate

[0033] In a reaction vessel, acrylonitrile, triallyl isocyanurate, and methyl methacrylate are uniformly mixed in a weight ratio of 35-85:5-30:0-5 to obtain a monomer mixture, and then 0.79-1.54% of an initiator and 417-1530% of a pure water solvent, based on the weight of the monomer mixture, are added and stirred uniformly. The mixture is then reacted at a temperature of 70-75° C. and a stirring speed of 600-1000 rpm for 3-6 hours, filtered, and the obtained solid is successively washed with ethanol and deionized water, and then dried in an oven at a temperature of 40-60° C. for 12-24 hours to obtain the polymer microsphere substrate (PAN-TAIC-X);

[0034] In the present invention, the main role of acrylonitrile and triallyl isocyanurate monomers in the preparation of walnut-shaped porous carbon composite microspheres is that they copolymerize into spheres under the initiation of an initiator. The spheres constitute the polymer microsphere base in the subsequent preparation process and are partially decomposed during the subsequent high-temperature carbonization to produce a walnut-shaped morphology with a concave and convex surface. In addition, N and O atoms are introduced into the polymer microsphere base.

[0035] Acrylonitrile and triallyl isocyanurate used in the present invention are both products currently sold on the market, such as acrylonitrile sold by Sinopharm Chemical Reagent Co., Ltd. under the trade name acrylonitrile, and triallyl isocyanurate sold by Shanghai Aladdin Biochemical Technology Co., Ltd. under the trade name triallyl isocyanurate.

[0036] In the present invention, methyl methacrylate (MMA) serves as the third monomer. Its primary function in preparing walnut-shaped porous carbon composite microspheres is to adjust the composition and internal pore structure of the composite microspheres. The present invention can utilize different types and amounts of the third monomer to alter the degree of polymerization and crosslinking of the composite microspheres, thereby obtaining walnut-shaped porous carbon composite microspheres of varying morphology and composition.

[0037] The methyl methacrylate third monomer used in the present invention can be replaced by one or more third monomers selected from styrene (St), divinylbenzene (DVB), ethylene glycol dimethacrylate (EGDMA), diallyl maleate (DAM), and cyclotrimethylolpropane formal acrylate (CTFA). The third monomers used in the present invention are all products currently available on the market, such as methyl methacrylate sold under the trade name methyl methacrylate by Sinopharm Chemical Reagent Co., Ltd. and ethylene glycol dimethacrylate sold under the trade name ethylene glycol dimethacrylate by Guangzhou Sanwang Chemical Materials Co., Ltd.

[0038] In the present invention, when the amounts of triallyl isocyanurate and the third monomer are within the range, if the amount of acrylonitrile monomer is less than 35, these monomers cannot be copolymerized into spheres; if the amount of acrylonitrile is greater than 85, the prepared polymer microspheres are severely agglomerated, and even the microsphere morphology cannot be maintained in step B; therefore, the amount of acrylonitrile is appropriately 35 to 85.

[0039] When the amounts of acrylonitrile and the third monomer are within the above ranges, if the amount of triallyl isocyanurate monomer is less than 5, the prepared polymer microspheres will be severely agglomerated, and even the microsphere morphology cannot be maintained in step B; if the amount of triallyl isocyanurate monomer is greater than 30, these monomers cannot be copolymerized into spheres; therefore, the appropriate amount of triallyl isocyanurate is 5 to 30.

[0040] When the amounts of acrylonitrile and triallyl isocyanurate are within the range, the amount of the third monomer can be 0; if the amount of the third monomer is higher than 5, concave-convex microspheres cannot be formed in step B, affecting the surface morphology of the polymer microspheres; therefore, it is desirable that the amount of the third monomer be 0 to 5.

[0041] The initiator used in the present invention is one or more initiators selected from azobisisobutylamidine hydrochloride, potassium persulfate, ammonium persulfate or sodium persulfate, all of which are products currently sold on the market, such as azobisisobutylamidine hydrochloride sold by Shanghai MacLean Biochemical Technology Co., Ltd. under the trade name azobisisobutylamidine hydrochloride.

[0042] In the present invention, it is not advisable to use an initiator amount exceeding the above range, because if the initiator amount is less than 0.79%, the above-mentioned polymerization reaction will not be thorough; if the initiator amount is higher than 1.54%, agglomeration will occur; therefore, an initiator amount of 0.79 to 1.54% is appropriate, preferably 0.9 to 1.3%, and more preferably 1.0 to 1.2%.

[0043] In the present invention, pure water solvent should be understood as water whose impurity content is less than 0.01% by weight; it is not advisable to use a pure water solvent in an amount exceeding the said range, because if the amount of pure water is higher than 1530% by weight of the monomer mixture, the yield of polymer microspheres will be too low and resources will be wasted; if the amount of pure water is lower than 417% by weight of the monomer mixture, agglomeration will occur during the polymerization process; therefore, it is reasonable to use a pure water solvent in an amount of 417 to 1530% by weight of the monomer mixture.

[0044] In this step, acrylonitrile, triallyl isocyanurate, and the third monomer are reacted in a pure water solvent in the presence of an initiator at a temperature of 70-75°C and a stirring speed of 600-1000 rpm for 3-6 hours. Reaction temperatures, stirring speeds, and times exceeding the stated ranges are undesirable, as the polymerization reaction may not proceed adequately if the temperature is below 70°C or the reaction time is shorter than 3 hours. Furthermore, if the reaction temperature is above 75°C, the reactants may agglomerate. If the reaction time is longer than 6 hours, resources may be wasted. If the stirring speed is lower than 600 rpm, the polymerization reaction may be uneven, and spherical polymers with uniform particle sizes may not be obtained. If the stirring speed is higher than 1000 rpm, the polymer molecular weight may decrease, and spherical polymers with uniform particle sizes may not be obtained.

[0045] The filtration equipment used in this step is a filtration equipment commonly used in the art, such as the water flow vacuum pump filtration equipment sold by Qingdao Chuanghesheng Science and Education Instrument Equipment Co., Ltd. under the trade name Water Flow Vacuum Pump.

[0046] The solid obtained by filtration was washed successively with ethanol and deionized water in order to remove unreacted monomers and initiators.

[0047] The solid obtained by filtration needs to be dried in an oven at 40-60° C. for 12-24 hours. The main purpose is to remove ethanol and water to ensure that the water content of the solid is less than 0.01% by weight.

[0048] The reaction vessel used in this step is a three-necked flask equipped with an agitator and a condenser. The three-necked flask is a reaction vessel commonly used in this technical field. It is a product currently sold on the market, such as the oil bath sold by Shanghai Airan Instrument Co., Ltd. under the trade name EYELA oil bath; the oven used in this step is a product currently sold on the market, such as the product sold by Shanghai Senxin Experimental Instrument Co., Ltd. under the trade name Electric Constant Temperature Blast Drying Oven.

[0049] The polymer microsphere substrate obtained in this step was subjected to conventional morphological analysis using a scanning electron microscope sold by Hitachi under the trade name FlexSEM1000Ⅱ Scanning Electron Microscope. The analysis results showed that the polymer microspheres were monodisperse polymer microspheres with a particle size of 300 to 600 nm. For specific results, please refer to the examples in the specific implementation section.

[0050] B. Synthesis of polymer microspheres@sugar-Fe / Co / Ni composite microspheres

[0051] 1-5 parts by weight of the polymer microsphere base obtained in step A, 1-10 parts by weight of sugar, and 0.1-0.3 parts by weight of a metal salt are added to 50-60 parts by weight of pure water, and ultrasonic dispersion is performed using an ultrasonic device for 20-30 minutes. The mixture is then reacted in a reactor at a temperature of 180-200° C. for 8-12 hours, filtered, and the obtained solid is washed successively with ethanol and deionized water. The washed solid is dried in an oven at a temperature of 40-60° C. for 12-24 hours, thereby obtaining the polymer microsphere@sugar-Fe / Co / Ni composite microspheres;

[0052] In the present invention, the polymer microsphere substrate prepared in step A mainly serves as the substrate of the composite microspheres in the preparation of walnut-shaped porous carbon composite microspheres. It partially decomposes during subsequent high-temperature carbonization to produce a walnut-shaped morphology with a concave-convex surface, and also introduces N and O atoms.

[0053] The main role of sugar in preparing walnut-shaped porous carbon composite microspheres is to provide a partial carbon source. At the same time, it helps to reduce the density of the walnut-shaped porous carbon composite microspheres because it decomposes during the subsequent high-temperature carbonization, causing more oxygen-containing functional groups to be converted into gases and volatilized. The sugar used in the present invention is one or more sugars selected from polydextrose, glucose, D-xylose, oligoxylose, sucrose, lactose, oligofructose, or trehalose, all of which are currently available on the market, such as the polydextrose sold by the Youbaojia Food flagship store under the trade name polydextrose.

[0054] In the present invention, metal salt should be understood as a salt or hydrated salt consisting of a heavy metal ion and an organic acid radical or an inorganic acid radical.

[0055] The main function of the metal salt in preparing the walnut-shaped porous carbon composite microspheres is to provide metal ions so as to form a metal element or alloy in a subsequent high-temperature carbonization process, which is randomly embedded on the surface of the concave-convex carbon microspheres. At the same time, it can also form a hard template to prevent the pores in the porous carbon composite microspheres from collapsing. The metal salt used in the present invention is one or more metal salts selected from cobalt acetate tetrahydrate, nickel acetate tetrahydrate, ferric chloride hexahydrate, and cobalt chloride hexahydrate, all of which are products currently sold on the market, such as the product sold by Sinopharm Chemical Reagent Co., Ltd. under the trade name cobalt acetate tetrahydrate.

[0056] In this reaction, when the amounts of sugar and metal salt are within the range, if the amount of polymer microsphere base is less than 1 part by weight, the resulting polymer microspheres @ sugar-Fe / Co / Ni composite microspheres are uneven; if the amount of polymer microspheres is greater than 5 parts by weight, the resulting polymer microspheres @ sugar-Fe / Co / Ni composite microspheres exhibit adhesion and agglomeration; therefore, it is appropriate that the amount of polymer microsphere base is 1 to 5 parts by weight, preferably 1.5 to 3.5, and more preferably 2.0 to 3.0.

[0057] When the amounts of the polymer microsphere base and the metal salt are within the stated range, if the amount of sugar is less than 1 part by weight, the resulting polymer microspheres @ sugar-Fe / Co / Ni composite microspheres will exhibit adhesion and agglomeration; if the amount of sugar is greater than 10 parts by weight, the resulting polymer microspheres @ sugar-Fe / Co / Ni composite microspheres will be uneven in size; therefore, a reasonable amount of sugar is 1 to 10 parts by weight, preferably 2 to 8, and more preferably 4 to 6.

[0058] When the amounts of polymer microsphere substrate and sugar are within the stated ranges, if the amount of metal salt is less than 0.1 parts by weight, insufficient metal nanoparticles may be formed after subsequent carbonization. If the amount of metal salt is greater than 0.3 parts by weight, the resulting polymer microsphere@sugar-Fe / Co / Ni composite microspheres may adhere to each other. Therefore, an appropriate amount of metal salt is 0.1 to 0.3 parts by weight, preferably 0.15 to 0.25, and more preferably 0.16 to 0.22.

[0059] In this step, it is not advisable to use an amount of pure water solvent exceeding the stated range, because if the amount of pure water is less than 50 parts by weight, the polymer microspheres @ sugar-Fe / Co / Ni composite microspheres will agglomerate; if the amount of pure water is higher than 60 parts by weight, it will cause a waste of resources; therefore, it is advisable to use 50 to 60 parts by weight of pure water solvent.

[0060] In this step, the polymer microsphere substrate, sugar, and metal salt react in pure water at 180-200°C for 8-12 hours. Reaction temperatures and times exceeding the stated ranges are undesirable. Temperatures below 180°C or times shorter than 8 hours result in incomplete reactions. Temperatures above 200°C or times longer than 12 hours can lead to agglomeration and waste of resources.

[0061] The ultrasonic equipment used in the present invention is an Elmasonic E 120H ultrasonic equipment sold by the German Elmasonic Company under the trade name Ultrasonic Cleaner. The present invention performs ultrasonic dispersion according to the instruction manual of the ultrasonic equipment.

[0062] The reactor used in this step is a hydrothermal reactor with a polytetrafluoroethylene liner, which is a product currently sold on the market, for example, a product sold by Zhengzhou Oulei Instrument Equipment Co., Ltd. under the trade name Stainless Steel Hydrothermal Synthesis Reactor.

[0063] The polymer microspheres @ sugar-Fe / Co / Ni composite microspheres obtained in this step were subjected to conventional morphological analysis using a scanning electron microscope sold by Hitachi under the trade name FlexSEM1000Ⅱ scanning electron microscope. For specific results, please refer to the specific implementation section. The analysis results show that the polymer microspheres @ sugar-Fe / Co / Ni composite microspheres are monodisperse and uniformly sized microspheres with a particle size of 300 to 700 nm.

[0064] C. Carbonization

[0065] The polymer microspheres@sugar-Fe / Co / Ni composite microspheres obtained in step B are placed in an alumina crucible, and heated from room temperature to 700-900°C at a heating rate of 1.0-3.0°C / min in a tube furnace in an inert protective gas of nitrogen or argon, maintained at this temperature for 1.8-2.2 hours, and then naturally cooled to room temperature, thereby obtaining N,O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles.

[0066] This carbonization step is carried out in an inert protective gas of nitrogen or argon, the basic purpose of which is to protect the copolymer from being oxidized to form carbon and metal elements and alloys.

[0067] In this step, the heating rate is controlled at 1.0-3.0°C / min and the carbonization time is controlled at 1.8-2.2h because the heating rate and the carbonization time can ensure that the structure of the composite microspheres is stable and not destroyed, and the composite microspheres can be fully pyrolyzed and carbonized.

[0068] The present invention used a scanning electron microscope (SEM1000II, sold by Hitachi) under the trade name FlexSEM1000II Scanning Electron Microscope to analyze and characterize the carbonized product under conventional conditions. Specific results are described in the Specific Practice section. Microstructural analysis and characterization of the carbonized product was performed using a transmission electron microscope (JEM-2100F, sold by JEOL, Japan). Specific results are described in the Specific Practice section.

[0069] The analysis results listed in the specific implementation section show that the carbonized product is a carbon microsphere with some Fe / Co / Ni nanoparticles with a diameter of 20 to 90 nm randomly embedded on the surface of the concave-convex carbon microsphere. Micropores and mesopores with an average pore size of 3 to 9 nm are distributed inside the carbon microsphere. Its diameter is 290 to 380 nm and its specific surface area is 180 to 400 m 2 g -1 .

[0070] The present invention also relates to N, O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles prepared by the preparation method.

[0071] According to the test method described in Cage-like eggshell membrane-derived Co-CoxSy-Ni / N,S-codoped carbon composites for electromagnetic wave absorption (literature source: Chemical Engineering Journal 430(2022)132650), the walnut-shaped porous carbon composite microspheres of the present invention and paraffin are mixed evenly in a weight ratio of 1:5 to form a hollow coaxial circular sample (inner diameter of 3.04 mm and outer diameter of 7.00 mm). The wave absorption performance of the sample in the wavelength range of 2 to 18 GHz is tested by the coaxial method using Agilent PNAN5224A vector network analyzer. For specific results, please refer to the specific implementation part. The test results show that under the condition of matching thickness of 2.0 to 3.0 mm, the minimum reflection loss of this type of walnut-shaped porous carbon composite microspheres is -28.5 to -48.1 dB, and the optimal effective absorption bandwidth is 5.44 GHz.

[0072] [Beneficial Effects]

[0073] The beneficial technical effects of the present invention are:

[0074] Compared with the existing technology, the present invention adopts a green synthesis design process using water as a solvent to prepare porous carbon composite microspheres with uniform particle size. They have both magnetic Fe / Co / Ni nanoparticles and a walnut-shaped carbon microsphere matrix with a concave-convex surface morphology. AN-TAIC-X copolymer microspheres serve as the polymer microsphere substrate, providing both N and O heteroatoms and partially decomposing in the subsequent process to produce a pore structure that forms a concave-convex walnut-shaped morphology. Sugars not only provide a portion of the carbon source but also help reduce the material density. When these walnut-shaped porous carbon composite microspheres are used as electromagnetic wave absorbers, the material's attenuation ability and impedance matching can be effectively controlled by adjusting the type and ratio of the Fe / Co / Ni nanoparticles. Under the conditions of a mass ratio of walnut-shaped porous carbon composite microspheres to paraffin of 1:4 to 8 and a matching thickness of 2.0 to 3.0 mm, its minimum reflection loss is -28.5 to -48.1 dB, and the optimal effective absorption bandwidth is 5.44 GHz. This has opened up a new path for component adjustment, introduced defect engineering and morphology design, and realized a new preparation method for carbon composite microsphere absorbers with excellent electromagnetic wave absorption performance.

Brief Description of the Drawings

[0075] Figure 1Scanning electron microscope (SEM) images of the polymer microsphere substrate, polymer microsphere@sugar-Fe / Co / Ni composite microspheres, and N,O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles prepared in Examples 1-4;

[0076] In the picture:

[0077] a1-a4 are SEM images of the polymer microsphere substrates prepared in Examples 1-4, respectively;

[0078] b1-b4 are SEM images of polymer microspheres@sugar-Fe / Co / Ni composite microspheres;

[0079] c1-c4 are SEM images of N,O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles.

[0080] Figure 2 1 is a transmission electron microscope (TEM) image of the N,O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles prepared in Example 1;

[0081] Figure 3 : is the reflection loss graph of the N,O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles prepared in Example 1;

[0082] Figure 4 : is the reflection loss graph of the N,O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles prepared in Example 2; [Specific implementation method]

[0083] The present invention will be better understood through the following examples.

[0084] Example 1: Preparation of walnut-shaped porous carbon composite microspheres of the present invention

[0085] The implementation steps of this embodiment are as follows:

[0086] A. Synthesis of polymer microsphere substrate

[0087] In a reaction vessel, acrylonitrile, triallyl isocyanurate and methyl methacrylate were mixed uniformly in a weight ratio of 85:10:0 to obtain a monomer mixture, and then 1.54% azobisisobutylamidine hydrochloride initiator and 1530% pure water solvent were added based on the weight of the monomer mixture, stirred uniformly, and then reacted at a temperature of 75°C and a stirring speed of 800 rpm for 6 hours. The solid was filtered, and the obtained solid was washed successively with ethanol and deionized water, and then dried in an oven at a temperature of 40°C for 24 hours to obtain the polymer microsphere substrate; a scanning electron micrograph of the polymer microsphere substrate is shown in the attached figure. Figure 1 ;

[0088] B. Synthesis of polymer microspheres@sugar-Fe / Co / Ni composite microspheres

[0089] 2 parts by weight of the polymer microsphere base obtained in step A, 4 parts by weight of polydextrose and 0.1 parts by weight of ferric chloride hexahydrate are added to 50 parts by weight of pure water, ultrasonically dispersed for 20 minutes using an ultrasonic device, and then reacted in a reactor at a temperature of 200°C for 10 hours, filtered, and the obtained solid was washed with ethanol and deionized water successively. The washed solid was dried in an oven at a temperature of 60°C for 12 hours to obtain the polymer microspheres @ sugar-Fe / Co / Ni composite microspheres; according to the method described in the specification of this application, the particle size of the polymer microspheres @ sugar-Fe / Co / Ni composite microspheres is 580-700 nm; the scanning electron microscope image of the polymer microspheres @ sugar-Fe / Co / Ni composite microspheres is shown in the attached Figure 1 ;

[0090] C. Carbonization

[0091] The polymer microspheres@sugar-Fe / Co / Ni composite microspheres obtained in step B were placed in an alumina crucible, heated from room temperature to 800°C in a tube furnace under nitrogen inert protective gas at a heating rate of 1.0°C / min, maintained at this temperature for 2.0 h, and then naturally cooled to room temperature, thereby obtaining N,O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles.

[0092] The scanning electron microscopy images of the N,O doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles prepared in this example are shown in the attached Figure 1 ; Its transmission electron microscope image is shown in the attached Figure 2 ; Its reflection loss diagram is shown in the attached Figure 3 ;

[0093] The N, O doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles are randomly embedded with some Fe / Co / Ni nanoparticles with a diameter of 20 to 90 nm on the surface of the concave-convex carbon microspheres. Micropores and mesopores with an average pore size of 3 to 9 nm are distributed inside the carbon microspheres. Its diameter is 290 to 340 nm and its specific surface area is 180 m 2 g -1 .

[0094] According to the method described in the specification of this application, the N,O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles prepared in this embodiment have a minimum reflection loss of -28.5dB and an optimal effective absorption bandwidth of 5.44GHz under the conditions of a weight ratio of 1:6 to paraffin and a matching thickness of 2.0mm.

[0095] Example 2: Preparation of walnut-shaped porous carbon composite microspheres of the present invention

[0096] The implementation steps of this embodiment are as follows:

[0097] A. Synthesis of polymer microsphere substrate

[0098] In a reaction vessel, acrylonitrile, triallyl isocyanurate, and diallyl maleate were mixed uniformly in a weight ratio of 35:5:0.5 to obtain a monomer mixture. 1.23% potassium persulfate initiator and 417% pure water solvent, based on the weight of the monomer mixture, were then added and stirred uniformly. The mixture was then reacted at a temperature of 72° C. and a stirring speed of 600 rpm for 4.2 hours. The mixture was filtered and the obtained solid was washed successively with ethanol and deionized water. The solid was then dried in an oven at a temperature of 60° C. for 12 hours to obtain the polymer microsphere substrate. A scanning electron micrograph of the polymer microsphere substrate is shown in the attached figure. Figure 1 ;

[0099] B. Synthesis of polymer microspheres@sugar-Fe / Co / Ni composite microspheres

[0100] 1 part by weight of the polymer microsphere base obtained in step A, 1 part by weight of D-xylose and 0.3 part by weight of cobalt acetate tetrahydrate are added to 60 parts by weight of pure water, ultrasonically dispersed for 24 minutes using an ultrasonic device, and then reacted in a reactor at a temperature of 190° C. for 9 hours, filtered, and the obtained solid was washed successively with ethanol and deionized water. The washed solid was dried in an oven at a temperature of 40° C. for 24 hours to obtain the polymer microspheres @ sugar-Fe / Co / Ni composite microspheres; according to the method described in the specification of this application, the particle size of the polymer microspheres @ sugar-Fe / Co / Ni composite microspheres is 300-440 nm; the scanning electron microscope image of the polymer microspheres @ sugar-Fe / Co / Ni composite microspheres is shown in the attached Figure 1 ;

[0101] C. Carbonization

[0102] The polymer microspheres @ sugar-Fe / Co / Ni composite microspheres obtained in step B were placed in an alumina crucible and heated from room temperature to 900°C at a heating rate of 2.0°C / min in an argon inert protective gas in a tube furnace. The mixture was kept at this temperature for 1.8 hours and then naturally cooled to room temperature to obtain N, O doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles. The scanning electron micrograph of the N, O doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles prepared in this embodiment is shown in the attached figure. Figure 1 ; Its reflection loss diagram is shown in the attached Figure 4 ;

[0103] According to the method described in the specification of this application, the N, O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles prepared in this embodiment are randomly embedded with some Fe / Co / Ni nanoparticles with a diameter of 20 to 90 nm on the surface of the concave-convex carbon microspheres. Micropores and mesopores with an average pore size of 3 to 9 nm are distributed inside the carbon microspheres. Its diameter is 340 to 380 nm, and its specific surface area is 400 m 2 g -1 .

[0104] According to the method described in the specification of this application, the N,O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles prepared in this embodiment have a minimum reflection loss of -42.4 dB and an optimal effective absorption bandwidth of 5.44 GHz under the conditions of a weight ratio of 1:4 to paraffin and a matching thickness of 2.4 mm.

[0105] Example 3: Preparation of walnut-shaped porous carbon composite microspheres of the present invention

[0106] The implementation steps of this embodiment are as follows:

[0107] A. Synthesis of polymer microsphere substrate

[0108] In a reaction vessel, acrylonitrile, triallyl isocyanurate and ethylene glycol dimethacrylate were mixed uniformly in a weight ratio of 62:20:3 to obtain a monomer mixture. 0.98% sodium persulfate initiator and 820% pure water solvent, based on the weight of the monomer mixture, were then added and stirred uniformly. The mixture was then reacted at a temperature of 70°C and a stirring speed of 900 rpm for 5 hours. The mixture was filtered and the obtained solid was washed successively with ethanol and deionized water. The solid was then dried in an oven at a temperature of 46°C for 20 hours to obtain the polymer microsphere substrate. A scanning electron micrograph of the polymer microsphere substrate is shown in the attached figure. Figure 1 ;

[0109] B. Synthesis of polymer microspheres@sugar-Fe / Co / Ni composite microspheres

[0110] 5 parts by weight of the polymer microsphere base obtained in step A, 7 parts by weight of glucose and 0.16 parts by weight of nickel acetate tetrahydrate are added to 55 parts by weight of pure water, ultrasonically dispersed for 30 minutes using an ultrasonic device, and then reacted for 8 hours at a temperature of 200°C in a reactor, filtered, and the obtained solid was washed with ethanol and deionized water successively. The washed solid was dried in an oven at a temperature of 46°C for 20 hours to obtain the polymer microspheres @ sugar-Fe / Co / Ni composite microspheres; according to the method described in the specification of this application, the particle size of the polymer microspheres @ sugar-Fe / Co / Ni composite microspheres is 430-560 nm; the scanning electron microscope image of the polymer microspheres @ sugar-Fe / Co / Ni composite microspheres is shown in the attached Figure 1 ;

[0111] C. Carbonization

[0112] The polymer microspheres @ sugar-Fe / Co / Ni composite microspheres obtained in step B were placed in an alumina crucible and heated from room temperature to 850°C at a heating rate of 1.0°C / min in a tube furnace in a nitrogen inert protective atmosphere. The mixture was kept at this temperature for 2.0 hours and then naturally cooled to room temperature. Thus, N, O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles were obtained. The scanning electron micrograph of the N, O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles prepared in this embodiment is shown in the attached figure. Figure 1 ;

[0113] According to the method described in the specification of this application, the N, O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles prepared in this embodiment are randomly embedded with some Fe / Co / Ni nanoparticles with a diameter of 20 to 90 nm on the surface of the concave-convex carbon microspheres. Micropores and mesopores with an average pore size of 3 to 9 nm are distributed inside the carbon microspheres. Its diameter is 320 to 360 nm, and its specific surface area is 260 m 2 g -1 .

[0114] According to the method described in the specification of this application, the N,O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles prepared in this embodiment have a minimum reflection loss of -35.2dB and an optimal effective absorption bandwidth of 5.44GHz under the conditions of a weight ratio of 1:8 to paraffin and a matching thickness of 3.0mm.

[0115] Example 4: Preparation of walnut-shaped porous carbon composite microspheres of the present invention

[0116] The implementation steps of this embodiment are as follows:

[0117] A. Synthesis of polymer microsphere substrate

[0118] In a reaction vessel, acrylonitrile, triallyl isocyanurate, and styrene were uniformly mixed in a weight ratio of 48:30:2 to obtain a monomer mixture. 0.79% ammonium persulfate initiator and 1230% pure water solvent, based on the weight of the monomer mixture, were then added and stirred uniformly. The mixture was then reacted at a temperature of 75° C. and a stirring speed of 1000 rpm for 3 hours. The mixture was filtered and the obtained solid was washed successively with ethanol and deionized water. The solid was then dried in an oven at a temperature of 52° C. for 18 hours to obtain the polymer microsphere substrate. A scanning electron micrograph of the polymer microsphere substrate is shown in the attached figure. Figure 1 ;

[0119] B. Synthesis of polymer microspheres@sugar-Fe / Co / Ni composite microspheres

[0120] 4 parts by weight of the polymer microsphere base obtained in step A, 10 parts by weight of sucrose and 0.22 parts by weight of cobalt chloride hexahydrate are added to 55 parts by weight of pure water, ultrasonically dispersed for 26 minutes using an ultrasonic device, and then reacted in a reactor at a temperature of 180° C. for 12 hours, filtered, and the obtained solid was washed successively with ethanol and deionized water. The washed solid was dried in an oven at a temperature of 52° C. for 16 hours to obtain the polymer microspheres @ sugar-Fe / Co / Ni composite microspheres; according to the method described in the specification of this application, the particle size of the polymer microspheres @ sugar-Fe / Co / Ni composite microspheres is 520-680 nm; the scanning electron microscope image of the polymer microspheres @ sugar-Fe / Co / Ni composite microspheres is shown in the attached Figure 1 ;

[0121] C. Carbonization

[0122] The polymer microspheres @ sugar-Fe / Co / Ni composite microspheres obtained in step B were placed in an alumina crucible and heated from room temperature to 700°C at a heating rate of 3.0°C / min in a tube furnace in a nitrogen inert protective atmosphere. The mixture was kept at this temperature for 2.0 hours and then naturally cooled to room temperature. Thus, N, O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles were obtained. The scanning electron micrograph of the N, O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles prepared in this embodiment is shown in the attached figure. Figure 1 ;

[0123] According to the method described in the specification of this application, the N, O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles prepared in this embodiment are randomly embedded with some Fe / Co / Ni nanoparticles with a diameter of 20 to 90 nm on the surface of the concave-convex carbon microspheres. Micropores and mesopores with an average pore size of 3 to 9 nm are distributed inside the carbon microspheres. Its diameter is 300 to 350 nm, and its specific surface area is 330 m 2 g -1 .

[0124] According to the method described in the specification of this application, the N,O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles prepared in this embodiment have a minimum reflection loss of -48.1dB and an optimal effective absorption bandwidth of 5.44GHz under the conditions of a weight ratio of 1:5 to paraffin and a matching thickness of 2.8mm.

Claims

1. A method for preparing N,O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles, characterized in that The preparation steps of the preparation method are as follows: A. Synthesis of polymer microsphere substrate In a reaction vessel, acrylonitrile, triallyl isocyanurate, and methyl methacrylate are uniformly mixed in a weight ratio of 35-85:5-30:0-5 to obtain a monomer mixture; 0.79-1.54% of an initiator and 417-1530% of a pure water solvent, based on the weight of the monomer mixture, are then added and stirred uniformly; and then reacted at a temperature of 70-75° C. and a stirring speed of 600-1000 rpm for 3-6 hours. The mixture is filtered, and the obtained solid is washed successively with ethanol and deionized water, and then dried in an oven at a temperature of 40-60° C. for 12-24 hours to obtain the polymer microsphere substrate; B. Synthesis of polymer microspheres@sugar-Fe / Co / Ni composite microspheres 1-5 parts by weight of the polymer microsphere base obtained in step A, 1-10 parts by weight of sugar, and 0.1-0.3 parts by weight of a metal salt are added to 50-60 parts by weight of pure water, and ultrasonic dispersion is performed using an ultrasonic device for 20-30 minutes. The mixture is then reacted in a reactor at a temperature of 180-200° C. for 8-12 hours, filtered, and the obtained solid is washed successively with ethanol and deionized water. The washed solid is dried in an oven at a temperature of 40-60° C. for 12-24 hours, thereby obtaining the polymer microsphere@sugar-Fe / Co / Ni composite microspheres; C. Carbonization The polymer microspheres@sugar-Fe / Co / Ni composite microspheres obtained in step B are placed in an alumina crucible and heated from room temperature to 700-900°C at a heating rate of 1.0-3.0°C / min in a tube furnace in an inert protective gas of nitrogen or argon. The temperature is maintained for 1.8-2.2 hours and then naturally cooled to room temperature to obtain N,O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles.

2. The preparation method according to claim 1, wherein In step A, the methyl methacrylate is replaced by one or more monomers selected from styrene, divinylbenzene, ethylene glycol dimethacrylate, diallyl maleate or cyclotrimethylolpropane formal acrylate.

3. The preparation method according to claim 1, wherein In step A, the initiator is one or more initiators selected from azobisisobutylamidine hydrochloride, potassium persulfate, ammonium persulfate or sodium persulfate.

4. The preparation method according to claim 1, characterized in that In step A, the polymer microspheres are monodisperse polymer microspheres with a particle size of 300-600 nm.

5. The preparation method according to claim 1, characterized in that In step B, the sugar is one or more sugars selected from polydextrose, glucose, D-xylose, xylooligosaccharides, sucrose, lactose, fructooligosaccharides or trehalose.

6. The preparation method according to claim 1, characterized in that In step B, the metal salt is one or more metal salts selected from cobalt acetate tetrahydrate, nickel acetate tetrahydrate, ferric chloride hexahydrate or cobalt chloride hexahydrate.

7. The preparation method according to claim 1, characterized in that In step B, the particle size of the polymer microspheres@sugar-Fe / Co / Ni composite microspheres is 300-700 nm.

8. N,O-doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles prepared according to the preparation method according to any one of claims 1 to 7.

9. The N,O doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles according to claim 8, characterized in that It is a carbon microsphere with some Fe / Co / Ni nanoparticles with a diameter of 20~90nm randomly embedded on the surface of the concave-convex carbon microsphere. Inside the carbon microsphere, there are micropores and mesopores with an average pore size of 3~9nm. Its diameter is 290~380nm and its specific surface area is 180~400m 2 g -1 .

10. The N,O doped walnut-shaped porous carbon composite microspheres loaded with Fe / Co / Ni nanoparticles according to claim 9, characterized in that Under the conditions of a weight ratio of the walnut-shaped porous carbon composite microspheres to paraffin of 1:4-8 and a matching thickness of 2.0-3.0 mm, its minimum reflection loss is -28.5-48.1 dB, and the optimal effective absorption bandwidth is 5.44 GHz.

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