A method for preparing a self-assembled structure of graphene-Fe coated hollow and / or porous microspheres

Abstract

The application belongs to the technical field of wave-absorbing and heat-insulating, and relates to a preparation method of graphene-Fe coated hollow and / or porous microspheres with a self-assembled structure. In a thermal reduction process, the graphene-Fe coated hollow and / or porous microspheres with the self-assembled structure effectively hinder the accumulation between graphene sheets, a large number of closed pore structures are generated inside, electromagnetic waves can form multiple reflections inside, and thus good wave-absorbing effect is achieved. Iron powder is in-situ synthesized on the surface of the graphene, and the dielectric loss and magnetic loss of the material are obviously improved. Through the joint action of various wave-absorbing mechanisms, the wave-absorbing performance of the material is improved.

Description

Technical Field

[0001] This invention belongs to the field of microwave absorption and heat insulation technology, and relates to a method for preparing graphene-Fe coated hollow and / or porous microspheres with a self-assembled structure. Background Technology

[0002] With the development of science and technology, modern society is surrounded by a massive amount of electronic products and advanced communication technologies, from smartphones and tablets to various smart home devices and even the widespread 5G base stations. This explosive growth of technologies has brought about increasingly serious electromagnetic pollution problems. Electromagnetic pollution has become a new source of pollution and is quietly becoming a new public nuisance in the 21st century, threatening not only personal information but also adversely affecting human health.

[0003] To address this challenge, researchers and engineers have innovatively developed microwave absorbing materials, a high-tech product designed to mitigate electromagnetic pollution. The working principle of microwave absorbing materials lies in their ability to cleverly absorb harmful electromagnetic wave energy and convert it into heat or other forms of energy release, thereby effectively weakening the propagation of electromagnetic waves and reducing their impact on the surrounding environment. The two most important factors in microwave absorbing materials are impedance matching and internal loss. Impedance matching maximizes the penetration of incident electromagnetic waves into the electromagnetic wave's interior, reducing reflection. Internal loss refers to the increased dielectric and magnetic losses within the material, reducing transmission. Traditional microwave absorbing materials include metals, metal particles, ferrites, and their alloys, which were widely used in the past due to their excellent magnetic loss characteristics. However, these materials typically suffer from drawbacks such as high density (large mass), poor acid and alkali resistance, and easy agglomeration, limiting their application potential in lightweight and miniaturized electronic devices. In contrast, novel dielectric loss materials, such as porous carbon, conductive carbon black, graphene, and carbon nanotubes, have revolutionized the field of microwave absorbing materials due to their low weight, corrosion resistance, and excellent electrical conductivity. However, single dielectric loss materials often struggle to achieve good impedance matching independently in practical applications, which directly limits their absorption efficiency. Summary of the Invention

[0004] This invention addresses the shortcomings of existing microwave absorbing materials by providing a method for preparing self-assembled graphene-Fe coated hollow and / or porous microspheres. The method uses graphene-coated hollow and / or porous microspheres and reduced iron to prepare self-assembled graphene-Fe coated hollow and / or porous microspheres with excellent heat insulation and microwave absorption properties.

[0005] One objective of this invention is achieved through the following technical solution:

[0006] A method for preparing self-assembled graphene-Fe coated hollow and / or porous microspheres includes the following steps:

[0007] Hollow and / or porous microspheres coated with graphene oxide (GO);

[0008] After thermal reduction, hollow and / or porous microspheres coated and modified with reduced graphene oxide were obtained;

[0009] Hollow and / or porous microspheres coated with reduced graphene oxide are then subjected to a reduction reaction, and iron is grown in situ on the surface of the reduced graphene oxide to obtain self-assembled graphene-Fe coated hollow and / or porous microspheres.

[0010] There are no particular restrictions on the number of graphene oxide layers; graphene oxide with 3 to 30 layers is preferred.

[0011] Hollow and / or porous microspheres can be listed as hollow glass microspheres (HGM), hollow ceramic microspheres, hollow metal microspheres, porous carbon, etc.

[0012] Preferably, the hollow and / or porous microspheres are hollow glass microspheres with a particle size of 5 to 500 μm and a wall thickness of 0.5 to 3 μm.

[0013] Preferably, the modified hollow and / or porous microspheres are obtained by grafting a silane coupling agent onto hollow and / or porous microspheres.

[0014] Preferably, the modified hollow and / or porous microspheres are obtained by hydroxylating hollow and / or porous microspheres and then grafting them with a silane coupling agent.

[0015] Preferably, hollow and / or porous microspheres are placed in an alkaline solution for reaction. After the reaction is completed, the microspheres are filtered, washed, and dried to obtain hydroxylated hollow and / or porous microspheres.

[0016] In the hydroxylation step, preferably, the alkaline solution is formed by dissolving an inorganic base in water, and the inorganic base includes, but is not limited to, one or more of sodium hydroxide, calcium hydroxide, potassium hydroxide, lithium hydroxide, and ammonium hydroxide.

[0017] In the hydroxylation step, preferably, the mass molar ratio of hollow and / or porous microspheres to alkali is 1 g: 0.001 to 1 mol.

[0018] In the hydroxylation step, preferably, the reaction is carried out at 45–95°C for 0.5–10 h; more preferably, the reaction is carried out at 50–90°C for 0.5–5 h. Even more preferably, the reaction is carried out under stirring conditions at a stirring speed of 100–1000 r / min.

[0019] Preferably, the steps of grafting silane coupling agent include: adding silane coupling agent to solvent, adjusting pH for hydrolysis, then adding hollow and / or porous microspheres or hydroxylated hollow and / or porous microspheres, reacting, and after solid-liquid separation, washing, and drying to obtain modified hollow and / or porous microspheres.

[0020] In the step of grafting silane coupling agents, the silane coupling agents include, but are not limited to, one or more of KH550, HK560, KH570, KH792, KH580, KH590, A-151, and A-171.

[0021] In the step of grafting silane coupling agents, preferably, the solvent is a mixture of water and a polar organic solvent, including but not limited to methanol, ethanol, acetone, acetonitrile, isopropanol, ethylene glycol, propylene glycol, etc. Preferably, the volume ratio of water to polar organic solvent is 1:0.5 to 5.

[0022] In the step of grafting silane coupling agent, preferably, the pH is adjusted to <7, and more preferably, the pH is adjusted to: 5 ≤ pH ≤ 6.8. There are no special requirements for the acid solution used to adjust the pH; any acidic solution that can adjust the pH is acceptable, such as hydrochloric acid solution, sulfuric acid solution, acetic acid solution, and hypochlorous acid solution.

[0023] In the step of grafting silane coupling agent, preferably, hydrolysis is carried out at 10-40°C for 0.5-5 hours.

[0024] In the step of grafting silane coupling agent, preferably, the mass ratio of hollow and / or porous microspheres or hydroxylated hollow and / or porous microspheres to silane coupling agent is 1:(0.2-10).

[0025] In the step of grafting silane coupling agent, preferably, the reaction is carried out at 45–95°C for 0.5–10 h; more preferably, the reaction is carried out at 50–90°C for 0.5–5 h. Even more preferably, the reaction is carried out under stirring conditions at a stirring speed of 100–1000 r / min.

[0026] Preferably, the step of coating the hollow and / or porous microspheres with graphene oxide includes: dispersing graphene oxide in water, adding the modified hollow and / or porous microspheres, reacting, and after the reaction is completed, separating the solid and liquid, washing, and drying to obtain the hollow and / or porous microspheres coated with graphene oxide.

[0027] In the step of coating and modifying hollow and / or porous microspheres with graphene oxide, preferably, each g of graphene oxide is dispersed in 10 to 1000 ml of water.

[0028] In the step of coating the hollow and / or porous microspheres with graphene oxide, preferably, the mass ratio of graphene oxide to the modified hollow and / or porous microspheres is 1:2 to 200; more preferably, it is 1:5 to 100.

[0029] In the step of coating the hollow and / or porous microspheres with graphene oxide, preferably, the reaction is carried out at 45–95°C for 0.5–10 h; more preferably, the reaction is carried out at 50–90°C for 0.5–5 h. Even more preferably, the reaction is carried out under stirring conditions at a stirring speed of 100–1000 r / min.

[0030] Preferably, the holding temperature for heat reduction is 200–400°C, more preferably 250–350°C; and the holding time for heat reduction is 20–100 min, more preferably 40–80 min.

[0031] Preferably, the temperature is increased to the heat reduction holding temperature at a rate of 5–15 °C / min.

[0032] Preferably, the reduction reaction step includes: placing the reduced graphene oxide-coated hollow and / or porous microspheres in a ferric salt or ferrous salt solution, and then adding a reducing agent with higher reducing power than Fe. 3+ or Fe 2+ The metal powder is reacted, allowed to stand, and the upper floating matter is collected, filtered, washed, and dried to obtain the final product.

[0033] In the reduction reaction step, preferably, the ferric salt or ferrous salt is one or more of ferric nitrate, ferrous nitrate, ferrous sulfate, ferric sulfate, and ferrous chloride.

[0034] In the reduction reaction step, preferably, the reducing power is higher than that of Fe. 3+ or Fe 2+ The metal powder is one or more of zinc, magnesium, and calcium.

[0035] In the reduction reaction step, preferably, the mass molar ratio of the reduced graphene oxide-coated hollow and / or porous microspheres to the ferric or ferrous salt is 1 g: 0.05–1.0 mol.

[0036] In the reduction reaction step, preferably, the reducing power is higher than that of Fe. 3+ or Fe 2+ The amount of metal powder added is ≥ theoretically sufficient to make Fe 3+ or Fe 2+ The amount of metal powder completely reduced to Fe. Theoretically, this refers to calculations based on stoichiometry, that is, determining the minimum theoretical amount of metal powder to add according to the molar ratio of reactants to products in the chemical reaction equation.

[0037] In the reduction reaction step, preferably, the hollow and / or porous microspheres coated with reduced graphene oxide are placed in a ferric or ferrous salt solution and stirred at 10–40°C for 0.5–5 h. The stirring speed is 100–800 r / min.

[0038] In the reduction reaction step, preferably, a reducing agent with higher reducing power than Fe is added. 3+ or Fe 2+ The metal powder was stirred at 10–40°C for 0.5–5 hours. The stirring speed was 100–800 r / min.

[0039] The solid-liquid separation methods described in this article include, but are not limited to, centrifugation and vacuum filtration.

[0040] The drying methods described herein include, but are not limited to, vacuum drying and forced-air drying. Vacuum drying is preferred, which involves drying in a vacuum oven at 45–95°C for 3–30 hours.

[0041] Another objective of this invention is achieved through the following technical solution:

[0042] A self-assembled graphene-Fe coated hollow and / or porous microsphere is prepared by the above-described preparation method.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] 1. This invention modifies the surface of hollow and / or porous microspheres to load graphene oxide onto them, and then reduces the graphene oxide to rGO through high-temperature thermal reduction. Because the graphene oxide is coated on the hollow and / or porous microspheres, it effectively prevents the stacking between graphene sheets. Finally, through a reduction reaction, iron powder is grown in situ on the graphene surface, effectively preparing a graphene-Fe coated hollow and / or porous microsphere composite material with self-assembled structure and lightweight properties.

[0045] 2. In this invention, hollow and / or porous microspheres are first subjected to hydroxylation treatment, thereby increasing the grafting amount of silane coupling agent by hydroxylating the surface of the hollow and / or porous microspheres.

[0046] 3. The pore size of hollow and / or porous microspheres affects the microwave absorption and thermal insulation properties of composite materials. Generally speaking, within a certain range, the smaller the pore size of hollow and / or porous microspheres, the more times electromagnetic waves are reflected inside, which is more conducive to improving microwave absorption performance; and the smaller the pore size, the greater the thermal resistance and the better the thermal insulation performance.

[0047] 4. This invention synthesizes iron powder in situ on the surface of graphene, significantly improving both the dielectric and magnetic losses of the material. This promotes impedance matching on the material surface, allowing more electromagnetic waves to penetrate into the material's interior, thus enhancing overall microwave absorption performance. During the thermal reduction process, the graphene oxide coated with hollow glass microspheres effectively hinders the stacking of graphene sheets, generating numerous closed-cell structures within the material. Electromagnetic waves can undergo multiple reflections within this structure, achieving excellent microwave absorption. Furthermore, the abundant closed-cell structure increases thermal resistance, providing excellent thermal insulation. This material exhibits low density and excellent flame retardancy, perfectly meeting the surface microwave absorption requirements of stealth aircraft and high-energy microwave anechoic chambers: low density, thermal insulation, and microwave absorption. Attached Figure Description

[0048] Figure 1 The image shows a SEM image of the self-assembled graphene-Fe coated hollow glass microspheres prepared in Example 1. Detailed Implementation

[0049] The technical solution of the present invention will be further described and illustrated below with reference to specific embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are only for the purpose of helping to understand the present invention and are not intended to limit the specific scope of the present invention. Furthermore, the accompanying drawings used herein are merely for better illustrating the content disclosed in the present invention and do not limit the scope of protection. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used in the art, and the methods used in the embodiments are all conventional methods in the art.

[0050] Example 1

[0051] The self-assembled graphene-Fe coated hollow glass microspheres of this embodiment were prepared through the following steps:

[0052] (1) Hydroxylation treatment of hollow glass microspheres

[0053] 200 ml of 0.5 M NaOH aqueous solution and 10 g of HGM (particle size 50 μm, wall thickness 2 μm) were added to a 500 ml three-necked flask, and the mixture was stirred at 70 °C and 300 rpm for 1 h. After alkaline washing, the mixture was filtered, washed with water until neutral, and filtered again. The hydroxylated HGM was dried in a vacuum oven at 70 °C for 12 h to obtain OH-HGM.

[0054] (2) OH-HGM grafted with KH550

[0055] 200 ml of an ethanol-water solution (Vwater:Vethanol = 1:2) containing 10 g of KH550 was added to a three-necked flask. Hydrochloric acid solution was added to adjust the pH to 6.0, and hydrolysis was carried out at room temperature (25°C) for 2 hours. Then, 10 g of OH-HGM was added, and the reaction was stirred at 80°C and 300 rpm for 1.5 hours. After the reaction was complete, the mixture was filtered, and excess KH550 was removed with anhydrous ethanol. The filter cake was then dried in a vacuum oven at 70°C for 12 hours to obtain KH550-HGM.

[0056] (3) Graphene oxide-coated KH550-HGM

[0057] Weigh 0.4 g of GO and add it to 200 ml of deionized water, then sonicate for 30 min. Next, add 10 g of KH550-HGM and stir at 80 °C and 400 r / min for 1.5 h. After the reaction is complete, filter the mixture, wash with water, and dry in a vacuum oven at 70 °C for 12 h to obtain GO-HGM.

[0058] (4) High-temperature reduction of graphene oxide

[0059] Take 10g of GO-HGM and put it into a crucible. In a muffle furnace, raise the temperature to 300℃ at a heating rate of 10℃ / min and hold for 30min to obtain rGO-HGM.

[0060] (5) In-situ generation of iron from graphene oxide

[0061] Add 0.4 g rGO-HGM to 200 ml of 1 mol / L FeCl2 solution, stir at 300 r / min for 2 h at room temperature (25℃), slowly add 10 g of zinc powder granules (excess), stir at 300 r / min for 2 h at room temperature (25℃), let stand for 1 h, take the upper layer of rGO-Fe-HGM (floating), filter and remove ZnCl2 with anhydrous ethanol, put the filter cake in a vacuum oven at 70℃ and dry for 12 h to obtain rGO-Fe-HGM.

[0062] Figure 1 The image shows a SEM image of the self-assembled graphene-Fe coated hollow glass microspheres prepared in Example 1. It can be seen that the surface of the microspheres is coated with graphene-Fe.

[0063] Example 2

[0064] The only difference between Example 2 and Example 1 is that the HGM used in Example 2 has a particle size of 80 μm and a wall thickness of 2 μm. Everything else is the same as in Example 1.

[0065] Example 3

[0066] The only difference between Example 3 and Example 1 is that the HGM used in Example 3 has a particle size of 100 μm and a wall thickness of 2 μm. Everything else is the same as in Example 1.

[0067] Example 4

[0068] The only difference between Example 4 and Example 1 is that the HGM used in Example 4 has a particle size of 120 μm and a wall thickness of 2 μm. Everything else is the same as in Example 1.

[0069] Example 5

[0070] The only difference between Example 5 and Example 1 is that Example 5 did not undergo hydroxylation treatment, and specifically includes the following steps:

[0071] (1) OH-HGM grafted with KH550

[0072] 200 ml of an ethanol-water solution (Vwater:Vethanol = 1:2) containing 10 g of KH550 was added to a three-necked flask. Hydrochloric acid solution was added to adjust the pH to 6.0, and hydrolysis was carried out at room temperature (25°C) for 2 h. Then, 10 g of HGM (particle size 50 μm, wall thickness 2 μm) was added, and the reaction was stirred at 80°C and 300 rpm for 1.5 h. After the reaction was complete, the mixture was filtered, and excess KH550 was removed with anhydrous ethanol. The filter cake was then dried in a vacuum oven at 70°C for 12 h to obtain KH550-HGM.

[0073] The subsequent steps are the same as in Example 1.

[0074] Example 6

[0075] The self-assembled graphene-Fe coated hollow glass microspheres of this embodiment were prepared through the following steps:

[0076] (1) Hydroxylation treatment of hollow glass microspheres

[0077] 500 ml of 0.5 M potassium hydroxide aqueous solution and 20 g of HGM (particle size 50 μm, wall thickness 2 μm) were added to a 1000 ml three-necked flask, and the mixture was stirred at 80 °C and 400 rpm for 1.5 h. After alkaline washing, the mixture was filtered, washed with water until neutral, and filtered again. The hydroxylated HGM was dried in a vacuum oven at 80 °C for 12 h to obtain OH-HGM.

[0078] (2) OH-HGM grafted with KH560

[0079] 500 ml of an ethanol-water solution (Vwater:Vethanol = 1:2) containing 20 g of KH560 was added to a three-necked flask. Hydrochloric acid solution was added to adjust the pH to 5.5, and hydrolysis was carried out at room temperature (25°C) for 3 hours. Then, 20 g of OH-HGM was added, and the reaction was stirred at 85°C and 200 rpm for 2 hours. After the reaction was complete, the mixture was filtered, and excess KH560 was removed with anhydrous ethanol. The filter cake was then dried in a vacuum oven at 80°C for 12 hours to obtain KH560-HGM.

[0080] (3) Graphene oxide-coated KH560-HGM

[0081] Weigh 1.0 g of GO and add it to 400 ml of deionized water, then sonicate for 30 min. Next, add 20 g of KH560-HGM and stir at 85 °C and 300 r / min for 2 h. After the reaction is complete, filter, wash with water, and dry in a vacuum oven at 75 °C for 15 h to obtain GO-HGM.

[0082] (4) High-temperature reduction of graphene oxide

[0083] Take 20g of GO-HGM and put it into a crucible. In a muffle furnace, raise the temperature to 280℃ at a heating rate of 8℃ / min and hold for 50min to obtain rGO-HGM.

[0084] (5) In-situ generation of iron from graphene oxide

[0085] 1.0 g of rGO-HGM was added to 500 ml of 1 mol / L FeCl3 solution and stirred at 400 r / min for 3 h at room temperature (25 °C). 20 g of zinc powder granules (excess) was slowly added and stirred at 400 r / min for 3 h at room temperature (25 °C). After standing for 1 h, the upper layer of rGO-Fe-HGM (floating) was taken, filtered, and ZnCl2 was removed with anhydrous ethanol. The filter cake was placed in a vacuum oven at 75 °C and dried for 12 h to obtain rGO-Fe-HGM.

[0086] Comparative Example 1

[0087] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 did not undergo thermal reduction and iron reduction reactions. The specific steps are as follows:

[0088] (1) Hydroxylation treatment of hollow glass microspheres

[0089] 200 ml of 0.5 M NaOH aqueous solution and 10 g of HGM (particle size 50 μm, wall thickness 2 μm) were added to a 500 ml three-necked flask, and the mixture was stirred at 70 °C and 300 rpm for 1 h. After alkaline washing, the mixture was filtered, washed with water until neutral, and filtered again. The hydroxylated HGM was dried in a vacuum oven at 70 °C for 12 h to obtain OH-HGM.

[0090] (2) OH-HGM grafted with KH550

[0091] 200 ml of an ethanol-water solution (Vwater:Vethanol = 1:2) containing 10 g of KH550 was added to a three-necked flask. Hydrochloric acid solution was added to adjust the pH to 6.0, and hydrolysis was carried out at room temperature (25°C) for 2 hours. Then, 10 g of OH-HGM was added, and the reaction was stirred at 80°C and 300 rpm for 1.5 hours. After the reaction was complete, the mixture was filtered, and excess KH550 was removed with anhydrous ethanol. The filter cake was then dried in a vacuum oven at 70°C for 12 hours to obtain KH550-HGM.

[0092] (3) Graphene oxide-coated KH550-HGM

[0093] Weigh 0.4 g of GO and add it to 200 ml of deionized water, then sonicate for 30 min. Next, add 10 g of KH550-HGM and stir at 80 °C and 400 r / min for 1.5 h. After the reaction is complete, filter the mixture, wash with water, and dry in a vacuum oven at 70 °C for 12 h to obtain GO-HGM.

[0094] Comparative Example 2

[0095] The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 did not undergo an iron reduction reaction. The specific steps are as follows:

[0096] (1) Hydroxylation treatment of hollow glass microspheres

[0097] 200 ml of 0.5 M NaOH aqueous solution and 10 g of HGM were added to a 500 ml three-necked flask and stirred at 70 °C and 300 r / min for 1 h. After alkaline washing, the mixture was filtered, washed with water until neutral, and filtered again. The hydroxylated HGM was dried in a vacuum oven at 70 °C for 12 h to obtain OH-HGM.

[0098] (2) OH-HGM grafted with KH550

[0099] 200 ml of an ethanol-water solution (Vwater:Vethanol = 1:2) containing 10 g of KH550 was added to a three-necked flask. Hydrochloric acid solution was added to adjust the pH to 6.0, and hydrolysis was carried out at room temperature (25°C) for 2 hours. Then, 10 g of OH-HGM was added, and the reaction was stirred at 80°C and 300 rpm for 1.5 hours. After the reaction was complete, the mixture was filtered, and excess KH550 was removed with anhydrous ethanol. The filter cake was then dried in a vacuum oven at 70°C for 12 hours to obtain KH550-HGM.

[0100] (3) Graphene oxide-coated KH550-HGM

[0101] Weigh 0.4 g of GO and add it to 200 ml of deionized water, then sonicate for 30 min. Next, add 10 g of KH550-HGM and stir at 80 °C and 400 r / min for 1.5 h. After the reaction is complete, filter the mixture, wash with water, and dry in a vacuum oven at 70 °C for 12 h to obtain GO-HGM.

[0102] (4) High-temperature reduction of graphene oxide

[0103] Take 10g of GO-HGM and put it into a crucible. In a muffle furnace, raise the temperature to 300℃ at a heating rate of 10℃ / min and hold for 30min to obtain rGO-HGM.

[0104] Comparative Example 3

[0105] The difference between Comparative Example 3 and Example 1 is that the graphene oxide in Comparative Example 3 was not reduced. The specific steps are as follows:

[0106] (1) Hydroxylation treatment of hollow glass microspheres

[0107] 200 ml of 0.5 M NaOH aqueous solution and 10 g of HGM were added to a 500 ml three-necked flask and stirred at 70 °C and 300 r / min for 1 h. After alkaline washing, the mixture was filtered, washed with water until neutral, and filtered again. The hydroxylated HGM was dried in a vacuum oven at 70 °C for 12 h to obtain OH-HGM.

[0108] (2) OH-HGM grafted with KH550

[0109] 200 ml of an ethanol-water solution (Vwater:Vethanol = 1:2) containing 10 g of KH550 was added to a three-necked flask. Hydrochloric acid solution was added to adjust the pH to 6.0, and hydrolysis was carried out at room temperature (25°C) for 2 hours. Then, 10 g of OH-HGM was added, and the reaction was stirred at 80°C and 300 rpm for 1.5 hours. After the reaction was complete, the mixture was filtered, and excess KH550 was removed with anhydrous ethanol. The filter cake was then dried in a vacuum oven at 70°C for 12 hours to obtain KH550-HGM.

[0110] (3) Graphene oxide-coated KH550-HGM

[0111] Weigh 0.4 g of GO and add it to 200 ml of deionized water, then sonicate for 30 min. Next, add 10 g of KH550-HGM and stir at 80 °C and 400 r / min for 1.5 h. After the reaction is complete, filter the mixture, wash with water, and dry in a vacuum oven at 70 °C for 12 h to obtain GO-HGM.

[0112] (4) In-situ generation of iron from graphene oxide

[0113] Add 0.4 g of GO-HGM to 200 ml of 1 mol / L FeCl2 solution, stir at 300 r / min for 2 h at room temperature (25℃), slowly add 10 g of zinc powder granules (excess), stir at 300 r / min for 2 h at room temperature (25℃), let stand for 1 h, take the upper layer of GO-Fe-HGM (floating), filter and remove ZnCl2 with anhydrous ethanol, put the filter cake in a vacuum oven at 70℃ and dry for 12 h to obtain GO-Fe-HGM.

[0114] Comparative Example 4

[0115] The difference between Comparative Example 4 and Example 1 is that the graphene oxide in Comparative Example 4 is first reduced and then coated with KH550-HGM. The specific steps are as follows:

[0116] (1) Hydroxylation treatment of hollow glass microspheres

[0117] 200 ml of 0.5 M NaOH aqueous solution and 10 g of HGM were added to a 500 ml three-necked flask and stirred at 70 °C and 300 r / min for 1 h. After alkaline washing, the mixture was filtered, washed with water until neutral, and filtered again. The hydroxylated HGM was dried in a vacuum oven at 70 °C for 12 h to obtain OH-HGM.

[0118] (2) OH-HGM grafted with KH550

[0119] 200 ml of an ethanol-water solution (Vwater:Vethanol = 1:2) containing 10 g of KH550 was added to a three-necked flask. Hydrochloric acid solution was added to adjust the pH to 6.0, and hydrolysis was carried out at room temperature (25°C) for 2 hours. Then, 10 g of OH-HGM was added, and the reaction was stirred at 80°C and 300 rpm for 1.5 hours. After the reaction was complete, the mixture was filtered, and excess KH550 was removed with anhydrous ethanol. The filter cake was then dried in a vacuum oven at 70°C for 12 hours to obtain KH550-HGM.

[0120] (3) High-temperature reduction of graphene oxide

[0121] Weigh 10g of GO and place it in a crucible. In a muffle furnace, raise the temperature to 300℃ at a heating rate of 10℃ / min and hold for 30min to obtain rGO.

[0122] (4) rGO encapsulation of KH550-HGM

[0123] Weigh 0.4 g of rGO and add it to 200 ml of deionized water, then sonicate for 30 min. Next, add 10 g of KH550-HGM and stir at 80 °C and 400 r / min for 1.5 h. After the reaction is complete, filter the mixture, wash with water, and dry in a vacuum oven at 70 °C for 12 h to obtain rGO-HGM.

[0124] (5) In-situ generation of iron from graphene oxide

[0125] Add 0.4 g rGO-HGM to 200 ml of 1 mol / L FeCl2 solution, stir at 300 r / min for 2 h at room temperature (25℃), slowly add 10 g of zinc powder granules (excess), stir at 300 r / min for 2 h at room temperature (25℃), let stand for 1 h, take the upper layer of rGO-Fe-HGM (floating), filter and remove ZnCl2 with anhydrous ethanol, put the filter cake in a vacuum oven at 70℃ and dry for 12 h to obtain rGO-Fe-HGM.

[0126] Comparative Example 5

[0127] The difference between Comparative Example 5 and Example 1 is that the HGM in Comparative Example 5 was not modified. The specific steps are as follows:

[0128] (1) Graphene oxide-coated HGM

[0129] Weigh 0.4 g of GO and add it to 200 ml of deionized water, then sonicate for 30 min. Next, add 10 g of HGM (particle size 50 μm, wall thickness 2 μm) and stir at 80 °C and 400 r / min for 1.5 h. After the reaction is complete, filter, wash with water, and dry in a vacuum oven at 70 °C for 12 h to obtain GO-HGM.

[0130] (4) High-temperature reduction of graphene oxide

[0131] Take 10g of GO-HGM and put it into a crucible. In a muffle furnace, raise the temperature to 300℃ at a heating rate of 10℃ / min and hold for 30min to obtain rGO-HGM.

[0132] (5) In-situ generation of iron from graphene oxide

[0133] Add 0.4 g of rGO-HGM to 200 ml of 1 mol / L FeCl2 solution and stir at 300 r / min for 2 h at room temperature (25 °C). Slowly add 10 g of zinc powder granules (excess) and stir at 300 r / min for 2 h at room temperature (25 °C). Let stand for 1 h, take the upper layer of rGO-Fe-HGM (floating), filter it and remove ZnCl2 with anhydrous ethanol. Place the filter cake in a vacuum oven at 70 °C and dry for 12 h to obtain rGO-Fe-HGM.

[0134] The products of Examples 1-6 and Comparative Examples 1-5 were prepared into 4 mm thick samples (the samples and paraffin were placed in a mold at a volume ratio of 1:1 and pressed into a film). The absorption performance was analyzed using a vector network analyzer at 8-18 GHz. The maximum absorption performance and the frequency bandwidth >10 dBd are shown in Table 1.

[0135] The sample was placed on a heating platform at a constant temperature of 80℃ and heated at room temperature for 1 hour. Then, the surface temperature of the material was measured using an infrared thermometer. The specific test results are shown in Table 1.

[0136] Table 1. Wave absorption and thermal insulation performance data of the materials in the examples and comparative examples.

[0137]

[0138] As shown in Table 1, Comparative Example 2 exhibits enhanced wave absorption capability compared to Comparative Example 1. Both in terms of maximum absorption capability and the range exceeding 10 dB, Comparative Example 2 demonstrates superior absorption performance. This is because the graphene oxide coating the hollow glass microspheres effectively hinders the stacking of graphene sheets during thermal reduction, generating numerous closed-pore structures internally, thus enhancing absorption performance. Comparative Example 2 and Example 1 also show that in-situ synthesis of iron powder on the graphene surface positively impacts both the real and imaginary parts of magnetic loss. The material's dielectric and magnetic losses are significantly improved, promoting impedance matching at the material surface and allowing more electromagnetic waves to penetrate the material's interior, reducing internal losses and overall improving absorption performance. Comparative Examples 4 and 3 show that graphene oxide reduction can improve the microwave absorption performance of the material to some extent. However, comparing Comparative Example 4 and Example 1, it is evident that when graphene oxide is thermally reduced without being coated with hollow glass microspheres, graphene oxide accumulates. Therefore, although Comparative Example 4 underwent thermal reduction, its microwave absorption performance is still inferior to that of Example 1. A comparison of Comparative Example 5 and Example 1 shows that only after HGM is treated with hydroxyl groups and modified with a silane coupling agent can graphene oxide successfully coat the HGM surface, hindering the accumulation of graphene sheets during thermal reduction and thus improving the material's microwave absorption performance.

[0139] As seen in Examples 1, 2, 3, and 4, the absorption capacity decreases as the pore size of the glass microspheres increases. This is because smaller pore sizes enhance the multiple reflections of electromagnetic waves within the microspheres, thus improving absorption performance, while larger pore sizes reduce absorption. Example 5, which uses only a silane coupling agent, shows a slight decrease in absorption performance compared to Example 1.

[0140] Table 1 shows that the thermal insulation performance is mainly related to the pore size of the hollow glass microspheres. The smaller the pore size, the greater the thermal resistance. Therefore, Comparative Example 1 and Example 1 have the same thermal insulation performance, while the thermal insulation performance of Examples 1, 2, 3, and 4 decreases sequentially. All materials achieve a flame retardant performance of V0. Furthermore, the density of all materials is less than 0.3 g / cm³. 3 It is a very lightweight material.

[0141] All aspects, embodiments, and features of this invention should be considered illustrative in all respects and not limiting of the invention; the scope of the invention is defined only by the claims. Other embodiments, modifications, and uses will become apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0142] In the preparation method of this invention, the order of the steps is not limited to the listed order. For those skilled in the art, variations in the order of the steps without creative effort are also within the scope of protection of this invention. Furthermore, two or more steps or actions can be performed simultaneously.

[0143] Finally, it should be noted that the specific embodiments described herein are merely illustrative examples of the invention and are not intended to limit the implementation of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them; it is neither necessary nor possible to exemplify all embodiments here. However, these obvious variations or modifications derived from the essential spirit of the invention still fall within the scope of protection of the invention, and interpreting them as any additional limitation would contradict the spirit of the invention.

Claims

1. A method for preparing graphene-Fe coated hollow and / or porous microspheres with a self-assembled structure, characterized in that, Includes the following steps: Hollow and / or porous microspheres coated with graphene oxide; After thermal reduction, hollow and / or porous microspheres coated and modified with reduced graphene oxide were obtained; Hollow and / or porous microspheres coated with reduced graphene oxide are then subjected to a reduction reaction to grow iron in situ on the surface of reduced graphene oxide, resulting in self-assembled graphene-Fe coated hollow and / or porous microspheres. The modified hollow and / or porous microspheres are obtained by grafting a silane coupling agent onto hollow and / or porous microspheres, or by hydroxylating hollow and / or porous microspheres and then grafting a silane coupling agent onto them.

2. The preparation method according to claim 1, characterized in that, Hollow and / or porous microspheres are placed in an alkaline solution for reaction. After the reaction is completed, the microspheres are filtered, washed, and dried to obtain hydroxylated hollow and / or porous microspheres. The steps of grafting silane coupling agents include: adding the silane coupling agent to a solvent, adjusting the pH to carry out hydrolysis, then adding hollow and / or porous microspheres or hydroxylated hollow and / or porous microspheres, reacting, and after solid-liquid separation, washing, and drying to obtain the modified hollow and / or porous microspheres.

3. The preparation method according to claim 2, characterized in that, In the hydroxylation step, the mass molar ratio of hollow and / or porous microspheres to alkali is 1 g: 0.001 to 1 mol; And / or, the hydroxylation treatment is carried out at 45–95 °C for 0.5–10 h.

4. The preparation method according to claim 2, characterized in that, In the step of grafting silane coupling agent, the solvent is a mixture of water and polar organic solvent, and the volume ratio of water to polar organic solvent is 1:0.5 to 5. And / or, adjust the pH to: 5 ≤ pH ≤ 6.8; And / or, adjust the pH and hydrolyze at 10–40℃ for 0.5–5 hours; And / or, the mass ratio of hollow and / or porous microspheres or hydroxylated hollow and / or porous microspheres to silane coupling agent is 1:(0.2-10); And / or, the reaction of the grafted silane coupling agent is carried out at 45–95°C for 0.5–10 h.

5. The preparation method according to claim 1, characterized in that, The steps for coating and modifying hollow and / or porous microspheres with graphene oxide include: dispersing graphene oxide in water, adding the modified hollow and / or porous microspheres, reacting, and after the reaction is completed, separating the solid and liquid, washing, and drying to obtain the graphene oxide-coated and modified hollow and / or porous microspheres.

6. The preparation method according to claim 5, characterized in that, In the step of coating and modifying hollow and / or porous microspheres with graphene oxide, each gram of graphene oxide is dispersed in 10 to 1000 ml of water; And / or, the mass ratio of graphene oxide to modified hollow and / or porous microspheres is 1:2 to 200; And / or, the coating step reaction is carried out at 45–95°C for 0.5–10 h.

7. The preparation method according to claim 1, characterized in that, The holding temperature for heat reduction is 200–400℃, and the holding time for heat reduction is 20–100 min. And / or, heat to the thermal reduction holding temperature at a rate of 5–15 °C / min.

8. The preparation method according to claim 1, characterized in that, The reduction reaction involves placing hollow and / or porous microspheres coated with reduced graphene oxide in a solution of ferric or ferrous salts, followed by adding a reducing agent with higher reducing power than Fe. 3+ or Fe 2+ The metal powder is reacted, allowed to stand, and the upper floating matter is collected, filtered, washed, and dried to obtain the final product.

9. The preparation method according to claim 8, characterized in that, The ferric salt or ferrous salt is one or more of ferric nitrate, ferrous nitrate, ferrous sulfate, ferric sulfate, ferric chloride, and ferrous chloride; And / or, with reducing power higher than Fe 3+ or Fe 2+ The metal powder is one or more of zinc, magnesium, and calcium; And / or, the mass molar ratio of the hollow and / or porous microspheres coated with reduced graphene oxide to the ferric or ferrous salt is 1 g: 0.05–1.0 mol; And / or, the hollow and / or porous microspheres coated with reduced graphene oxide are placed in a solution of ferric salt or ferrous salt and stirred at 10–40 °C for 0.5–5 h; And / or, adding substances with reducing properties higher than Fe 3+ or Fe 2+ The metal powder was stirred and reacted at 10–40°C for 0.5–5 hours.

10. A self-assembled graphene-Fe coated hollow and / or porous microsphere, characterized in that, It is prepared by the preparation method described in claim 1.

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