An intrinsic graphene preform with tunable electromagnetic properties in the X-band and its preparation method thereof

Abstract

This invention discloses an intrinsic graphene preform with tunable X-band electromagnetic properties and its preparation method, belonging to the field of functional materials technology. The preparation method is as follows: an intrinsic graphene aqueous suspension is prepared; an intrinsic graphene dispersion is prepared; a gelling agent and a pore-forming agent are added to the dispersion, and ultrasonic treatment is performed to obtain an intrinsic graphene mixed solution; the dispersion is sheared to obtain an intrinsic graphene aqueous solution; a foam stabilizer is added to the intrinsic graphene aqueous solution, and ultrasonic treatment is performed to obtain an intrinsic graphene hydrogel; the intrinsic graphene hydrogel is frozen to obtain intrinsic graphene hydrogel ice crystals, which are then dried to obtain an intrinsic graphene preform. The intrinsic graphene preform prepared by the above method, as an intrinsic graphene preform for coping with complex external electromagnetic environment changes and developing highly integrated homogeneous adaptive electromagnetic composite materials in the X-band, can solve the defects existing when graphene oxide is used as a preform, and further addresses the problems of poor forming effect and high preparation difficulty of existing intrinsic graphene preforms based on the above preparation method.

Description

Technical Field

[0001] This invention belongs to the field of functional materials technology, specifically relating to an intrinsic graphene preform with tunable electromagnetic properties in the X-band and its preparation method. Background Technology

[0002] With the rapid development of 5G communication, satellite phones, radio transmitters, and radar detectors, developing highly integrated homogeneous adaptive electromagnetic materials in the X-band is an effective way to cope with changes in complex external electromagnetic environments. Graphene, with its unique nanoscale structure, excellent mechanical properties, large specific surface area, good microwave absorption, and excellent electrothermal transfer characteristics, has broad application prospects in electromagnetic materials, supercapacitors, and other fields. Among them, graphene preforms, as an important form of graphene assembly, have characteristics such as high porosity, excellent electrical conductivity, and designable microstructure. Using them as reinforcements in metal matrix composites allows for the effective utilization of the tunable microstructure and electromagnetic properties of graphene preforms. This ensures that the prepared metal matrix composites can autonomously control the impedance matching between the material and air and achieve tunable electromagnetic properties, which places higher demands on the microstructure and electromagnetic properties of graphene preforms.

[0003] For example, Chinese patent CN113148996A discloses a method for preparing three-dimensional reduced graphene oxide porous microwave absorbing materials by mixing an aqueous solution of graphene oxide, a reducing agent, and an antifreeze agent with magnetic stirring, ultrasonic dispersion, freezing, room temperature thawing, and freeze-thaw cycles. By controlling the pore size and volume of the absorbing material, effective absorption of 6–18 GHz can be achieved. Currently, the raw material for preparing three-dimensional porous graphene preforms is graphene oxide. The numerous oxygen-containing functional groups on its surface cause it to spontaneously form a honeycomb network structure when assembled into a three-dimensional preform, which limits its microstructure control and electromagnetic wave response control. In addition, the numerous oxygen-containing functional groups and defects on the surface of graphene oxide cannot be completely removed after reduction treatment, causing its conductivity to lag behind its intrinsic properties. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, the present invention aims to provide an intrinsic graphene preform with tunable electromagnetic properties in the X-band and its preparation method. This solves the technical problem that the raw material for graphene preforms in current composite materials is graphene oxide, which has a large number of oxygen-containing functional groups that limit the control of microstructure and electromagnetic functionality when assembled into a three-dimensional preform. Furthermore, the large number of oxygen-containing functional groups and defects cannot be completely removed after reduction treatment, resulting in conductivity and functionality that lag behind intrinsic properties.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] This invention provides a method for preparing an intrinsic graphene preform with tunable electromagnetic properties in the X-band, comprising the following steps:

[0007] S1: Take raw graphite powder and use liquid phase exfoliation method to perform multiple ultrasonic exfoliations to obtain intrinsic graphene water-based suspension; take the supernatant of intrinsic graphene water-based suspension and use rotary evaporation method to prepare intrinsic graphene dispersion.

[0008] S2: Add gelling agent and pore-forming agent to intrinsic graphene dispersion, and perform ultrasonic treatment to obtain intrinsic graphene mixed solution;

[0009] S3: Shear the intrinsic graphene mixture to obtain an intrinsic graphene aqueous solution;

[0010] S4: Add a foam stabilizer to an intrinsic graphene aqueous solution and perform ultrasonic treatment to obtain an intrinsic graphene hydrogel.

[0011] S5: Freeze the intrinsic graphene hydrogel to obtain intrinsic graphene hydrogel ice crystals, and dry the intrinsic graphene hydrogel ice crystals to obtain an intrinsic graphene preform.

[0012] In one embodiment, in step S1, the concentration of the intrinsic graphene dispersion is 5–15 mg / ml.

[0013] In one embodiment, in S1, the mass ratio of graphene to raw graphite powder in the supernatant of the intrinsic graphene aqueous suspension is 1:8 to 14.

[0014] In one embodiment, in S1, the intrinsic graphene in the intrinsic graphene dispersion has a sheet size of 5–15 μm and a thickness of 0.5–1.5 nm, with a Raman defect degree of I. D / I G The value is between 0.1 and 0.4;

[0015] The viscosity of the supernatant is 1.30–1.52 cP, and the surface tension is 65–68 mN / m.

[0016] In one embodiment, in step S2, the gelling agent is polyvinyl alcohol or sodium carboxymethyl cellulose, and the mass ratio of intrinsic graphene to gelling agent in the intrinsic graphene mixed solution is 4 to 16:1.

[0017] In one embodiment, in step S2, the pore-forming agent is sodium dodecyl sulfate or polystyrene, and the mass ratio of intrinsic graphene to pore-forming agent in the intrinsic graphene mixed solution is 1:0 to 8.

[0018] In one embodiment, in step S3, the rotational speed of the shearing process is 800–2600 rpm, and the shearing time is 2–22 min.

[0019] In one embodiment, in step S4, the foam stabilizer is one or more of sodium riboflavin phosphate and sodium dodecylbenzene sulfonate, and the mass ratio of intrinsic graphene to foam stabilizer in the intrinsic graphene hydrogel is 15 to 40:1.

[0020] In one embodiment, in step S5, the freezing temperature is -180 to -20°C, the freezing time is 10 to 720 minutes, and the drying time is 36 to 48 hours.

[0021] The present invention also provides an intrinsic graphene preform prepared by the method described above for preparing an intrinsic graphene preform with tunable X-band electromagnetic properties.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] This invention provides a method for preparing an intrinsic graphene preform with tunable X-band electromagnetic properties. The method involves preparing an intrinsic graphene aqueous suspension by liquid-phase exfoliation of graphite powder, followed by the preparation of a high-concentration intrinsic graphene dispersion using rotary evaporation. Using this intrinsic graphene dispersion with low Raman defect levels, few oxygen-containing functional groups, and low viscosity as raw material, a gelling agent and a pore-forming agent are added, followed by ultrasonic treatment to obtain an intrinsic graphene mixed solution. The addition of the gelling agent addresses the challenge of weak gelation of intrinsic graphene by increasing the viscosity of the intrinsic graphene dispersion. Since intrinsic graphene has few oxygen-containing functional groups, it can only form a cross-linked structure by combining with the carboxyl groups in the gelling agent and the hydroxyl groups in water, which facilitates the subsequent formation of the intrinsic graphene preform. The addition of the pore-forming agent addresses the problem of easy aggregation of intrinsic graphene and also controls the micropore structure of the intrinsic graphene preform. Finally, the intrinsic graphene mixed solution is subjected to high-speed... An intrinsic graphene aqueous solution is obtained through shearing. High-speed shearing is used to stir the intrinsic graphene mixture to form bubbles, creating a porous structure between the stacked intrinsic graphene sheets. The intrinsic graphene sheets are uniformly and tightly arranged around the bubbles, which helps to construct the three-dimensional network structure of the intrinsic graphene preform and to uniformly disperse the sheets. Then, a foam stabilizer is added and ultrasonic treatment is performed to obtain an intrinsic graphene hydrogel. The addition of the foam stabilizer is to stabilize the generated bubbles and ensure their uniform distribution, as well as to ensure the uniform distribution of the intrinsic graphene sheets. The hydrophilic groups of the foam stabilizer combine with water, and the hydrophobic groups combine with the intrinsic graphene sheets, which can simultaneously achieve the effects of stabilizing bubbles and uniformly dispersing intrinsic graphene sheets. Finally, the intrinsic graphene hydrogel is freeze-dried to obtain an intrinsic graphene preform. The intrinsic graphene preform with tunable X-band electromagnetic properties prepared by this invention can be used as a reinforcement for metal matrix composites.

[0024] In another aspect, this invention provides an intrinsic graphene preform with tunable X-band electromagnetic properties prepared using the above-described method. This preform can serve as a raw material for graphene preforms in the development of highly integrated homogeneous adaptive electromagnetic composite materials for coping with complex external electromagnetic environment changes. Besides the advantages of intrinsic graphene preforms, such as fewer defects and oxygen-containing functional groups, designable microstructure, tunable electromagnetic properties, and low preparation cost, the most important advantage is that the intrinsic graphene preform prepared using the above-described method exhibits good forming effect and a certain mechanical strength, solving the problems of poor forming effect and high preparation difficulty inherent in existing intrinsic graphene preforms. Attached Figure Description

[0025] Figure 1 Figures (a), (b), (c), and (d) are scanning electron microscope images of the intrinsic graphene preforms prepared in Examples 1, 3, 4, and 6 of this invention, respectively. Detailed Implementation

[0026] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0027] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0028] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0029] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0030] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0031] The intrinsic graphene preform proposed in this invention has advantages such as designable microstructure, tunable electromagnetic properties, and low preparation cost. On the one hand, the low defect rate and fewer oxygen-containing functional groups of intrinsic graphene endow it with the advantage of designable microstructure, giving it rich tunable properties in the field of electromagnetic functionality; on the other hand, it does not require subsequent heat treatment, resulting in low preparation cost. However, intrinsic graphene preforms suffer from poor forming effect and high preparation difficulty, which limits the application of intrinsic graphene in microstructure and electromagnetic property control. Therefore, it is necessary to explore a method for preparing intrinsic graphene preforms with certain mechanical strength and tunable electromagnetic properties.

[0032] This invention provides an intrinsic graphene preform with tunable X-band electromagnetic properties and its preparation method. The aim is to address the challenges of complex electromagnetic environment changes and develop highly integrated homogeneous adaptive electromagnetic composite materials in the X-band. This invention solves the problem that current graphene preforms are primarily made of graphene oxide, whose numerous oxygen-containing functional groups limit the control of microstructure and electromagnetic functionality when assembled into three-dimensional preforms. Furthermore, the numerous oxygen-containing functional groups and defects cannot be completely removed even after reduction treatment, resulting in conductivity and functionality that lag behind intrinsic properties. Intrinsic graphene preforms offer advantages such as fewer defects and oxygen-containing functional groups, designable microstructure, tunable electromagnetic properties, and low preparation cost. However, compared to graphene oxide, intrinsic graphene preforms suffer from poor forming effects and high preparation difficulty. Therefore, this invention provides a method for preparing intrinsic graphene preforms with tunable X-band electromagnetic properties.

[0033] This invention provides a method for preparing an intrinsic graphene preform with tunable electromagnetic properties in the X-band, comprising the following steps:

[0034] 1) Take raw graphite powder and use liquid phase exfoliation method to perform multiple ultrasonic exfoliations to obtain a black intrinsic graphene water-based suspension; take the supernatant and use rotary evaporation method to prepare an intrinsic graphene dispersion with a concentration of 5-15 mg / ml.

[0035] The mass ratio of graphene to raw graphite powder in the black intrinsic graphene supernatant is 1:8–14; the intrinsic graphene sheet size is 5–15 μm, the thickness is 0.5–1.5 nm, and the Raman defect level is I. D / I G The value is 0.1 to 0.4, the viscosity of the intrinsic graphene supernatant is 1.30 to 1.52 cP, and the surface tension is 65 to 68 mN / m.

[0036] 2) Add gelling agent and pore-forming agent to the intrinsic graphene dispersion prepared in step 1), and perform ultrasonic treatment to obtain an intrinsic graphene mixed solution;

[0037] The addition of a gelling agent increases the viscosity of the intrinsic graphene dispersion, forms a cross-linked structure, and facilitates the formation of the intrinsic graphene preform. A pore-forming agent is added to address the problem of easy aggregation of intrinsic graphene sheets and to regulate the micropore structure of the graphene preform. The gelling agent is polyvinyl alcohol or sodium carboxymethyl cellulose, and the mass ratio of intrinsic graphene to gelling agent in the intrinsic graphene mixed solution is 4–16:1. The gelling agent is added here to address the problem of weak gelation of intrinsic graphene and increase the viscosity of the intrinsic graphene dispersion. Since intrinsic graphene has relatively few oxygen-containing functional groups, This can only be achieved by combining the carboxyl groups in the gelling agent with the hydroxyl groups in the water to form a cross-linked structure, which helps in the subsequent formation of the intrinsic graphene preform; the pore-forming agent is sodium dodecyl sulfate or polystyrene, and the mass ratio of intrinsic graphene to pore-forming agent in the intrinsic graphene mixed solution is 1:0 to 8. Due to the low defects and fewer oxygen-containing functional groups on the surface of intrinsic graphene, the large van der Waals forces between the intrinsic graphene sheets cause the sheets to tend to stack together. The pore-forming agent is added here to solve the problem of easy aggregation of intrinsic graphene and can also control the micropore structure of the graphene preform.

[0038] The ultrasonic power is 40-200W, and the ultrasonic time is 3-20min;

[0039] 3) The intrinsic graphene mixed solution obtained in step 2) is subjected to high-speed shearing to obtain an intrinsic graphene aqueous solution;

[0040] The shearing speed is 800-2600 rpm and the shearing time is 2-22 min. This shearing action is to stir and form bubbles in the intrinsic graphene mixed solution, and form a porous structure between the stacked intrinsic graphene sheets. The intrinsic graphene sheets are uniformly and tightly arranged around the bubbles, which helps to construct the three-dimensional network structure of the intrinsic graphene preform and uniformly disperse the sheets.

[0041] 4) Add a foam stabilizer to the intrinsic graphene aqueous solution prepared in step 3) and perform ultrasonic treatment to obtain intrinsic graphene hydrogel;

[0042] The foam stabilizer is one or more of sodium riboflavin phosphate and sodium dodecylbenzene sulfonate. The mass ratio of intrinsic graphene to foam stabilizer in the intrinsic graphene hydrogel is 15-40:1. The foam stabilizer is added here to stabilize the bubbles generated in step 3), making the bubbles evenly distributed, and also to ensure the uniform distribution of intrinsic graphene sheets. The hydrophilic groups of the foam stabilizer combine with water, and the hydrophobic groups combine with the intrinsic graphene sheets, which can simultaneously achieve the effects of stabilizing bubbles and uniformly dispersing intrinsic graphene sheets. In short, the addition of the foam stabilizer achieves the effects of uniformly stabilizing bubbles and uniformly dispersing intrinsic graphene sheets.

[0043] The ultrasonic power is 40–200W, and the ultrasonic time is 3–15 minutes;

[0044] 5) Place the intrinsic graphene hydrogel prepared in step 4) into a freezing mold, put the mold into a freezing container for freezing, and obtain intrinsic graphene hydrogel ice crystals. Dry the intrinsic graphene hydrogel ice crystals to obtain intrinsic graphene preforms.

[0045] The freezing temperature is -180 to -20°C, the freezing time is 10 to 720 minutes, and the drying time is 36 to 48 hours.

[0046] The intrinsic graphene preforms prepared by the above method can be used as reinforcements for metal matrix composites. The electromagnetic properties of metal matrix composites can be controlled by introducing preforms with different electromagnetic properties into the matrix.

[0047] This invention overcomes the limitations of existing three-dimensional reduced graphene oxide microstructure and electromagnetic property control. It leverages the advantage of intrinsic graphene, which has fewer oxygen-containing functional groups, allowing for tunable microstructure in three-dimensional preforms. This invention prepares intrinsic graphene preforms with certain mechanical strength and tunable microstructure and electromagnetic properties. By adjusting the ratio of intrinsic graphene to pore-forming agent and the freezing temperature of the intrinsic graphene hydrogel, effective control over various properties such as wave transmission, electromagnetic shielding, and wave absorption can be achieved. Furthermore, the raw material used in the preparation of the preform is intrinsic graphene, which, compared to graphene oxide, has fewer structural defects and lower aqueous solution viscosity. D / I G The intrinsic graphene solution exhibits a value of 0.1–0.4 and a viscosity of 1.30–1.52 cP. Although intrinsic graphene solutions suffer from weak gelation and easy stacking of sheets, this invention effectively solves these problems by adding a gelling agent and a foaming agent. The prepared intrinsic graphene preform possesses certain mechanical strength; when the compressive strain is 50%, the compressive stress is 3–50 kPa, making it suitable as a reinforcement for metal matrix composites. Furthermore, this invention adds a foam stabilizer after high-speed shearing generates bubbles. This stabilizer serves two purposes: firstly, to stabilize the bubbles and ensure uniform bubble distribution; secondly, the foam stabilizer also acts as a surfactant, contributing to the uniform dispersion of the intrinsic graphene sheets.

[0048] In another aspect, this invention provides an intrinsic graphene preform prepared by the above method. By changing the ratio of intrinsic graphene to pore-forming agent and the freezing temperature of the intrinsic graphene hydrogel, an intrinsic graphene preform with certain mechanical properties and tunable electromagnetic properties is obtained. The density of this material is 0.03–0.07 g / cm³. 3The porosity is 90-96%. This material can achieve effective control over transmittance of 92%-98%, electromagnetic shielding effectiveness of ~45dB, and minimum electromagnetic wave absorption reflection loss of -50.7 to -10.6dB in the 8.2-12.4GHz band, which is significantly different from the control of single electromagnetic properties of three-dimensional reduced graphene oxide.

[0049] The principle of this invention is as follows: Since intrinsic graphene and graphene oxide have significant differences in defect degree, number of oxygen-containing functional groups, dispersion viscosity, and hydrophilicity, and graphene oxide has the characteristics of strong gelation and spontaneous formation of three-dimensional honeycomb network structure, which is completely different from the characteristics of weak gelation and layer stacking of intrinsic graphene, the preparation of intrinsic graphene preforms in this invention is different from the existing preparation methods of graphene oxide aerogels, breaking conventional thinking. Specifically, an intrinsic graphene aqueous suspension was prepared by liquid-phase exfoliation of graphite powder. A high-concentration intrinsic graphene dispersion was prepared by rotary evaporation. Using intrinsic graphene dispersions with low Raman defect levels, few oxygen-containing functional groups, and low viscosity as raw materials, a gelling agent and a pore-forming agent were added, followed by ultrasonic treatment to obtain an intrinsic graphene mixed solution. The addition of the gelling agent was to address the problem of weak gelation of intrinsic graphene and increase the viscosity of the intrinsic graphene dispersion. Since intrinsic graphene has few oxygen-containing functional groups, it can only form a cross-linked structure by combining with the carboxyl groups in the gelling agent and the hydroxyl groups in water, which is conducive to the subsequent formation of intrinsic graphene preforms. The addition of the pore-forming agent was to address the problem of easy aggregation of intrinsic graphene and to control the micropore structure of the intrinsic graphene preforms. Finally, the intrinsic graphene mixed solution was subjected to high-speed shearing to obtain intrinsic graphene water-soluble... High-speed shearing is used to stir the intrinsic graphene mixture to form bubbles, creating a porous structure between the stacked intrinsic graphene sheets. The intrinsic graphene sheets are uniformly and tightly arranged around the bubbles, which helps to construct the three-dimensional network structure of the intrinsic graphene preform and to uniformly disperse the sheets. Then, a foam stabilizer is added and ultrasonically treated to obtain an intrinsic graphene hydrogel. The addition of the foam stabilizer is to stabilize the generated bubbles and ensure their uniform distribution, as well as to ensure the uniform distribution of the intrinsic graphene sheets. The hydrophilic groups of the foam stabilizer combine with water, and the hydrophobic groups combine with the intrinsic graphene sheets, which can simultaneously achieve the effects of stabilizing bubbles and uniformly dispersing intrinsic graphene sheets. Finally, the intrinsic graphene hydrogel is freeze-dried to obtain the intrinsic graphene preform. The intrinsic graphene preform with tunable X-band electromagnetic properties prepared by this invention can be used as a reinforcement for metal matrix composites.

[0050] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0051] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0052] This invention relates to a method for preparing intrinsic graphene aqueous suspensions by liquid-phase exfoliation and for preparing high-concentration intrinsic graphene dispersions by rotary evaporation. Typical steps are illustrated below:

[0053] (1) Add 30 mg / ml of graphite powder and 1.5 mg / ml of riboflavin sodium phosphate to deionized water and stir ultrasonically at 300 W for 4.5 h to obtain a black intrinsic graphene water-based suspension.

[0054] (2) After standing for 48 hours, take the supernatant and prepare an intrinsic graphene dispersion with a concentration of 5-15 mg / ml by rotary evaporation. The rotary evaporation temperature is 60℃ and the time is 4 hours.

[0055] The above are publicly known technologies.

[0056] Example 1

[0057] This embodiment describes a method for preparing an intrinsic graphene preform with tunable electromagnetic properties in the X-band. The specific steps are as follows:

[0058] Step 1: Take 5 mg / ml of intrinsic graphene dispersion, add polyvinyl alcohol and sodium dodecyl sulfate to the intrinsic graphene dispersion according to the intrinsic graphene to polyvinyl alcohol mass ratio of 4:1 and the intrinsic graphene to sodium dodecyl sulfate mass ratio of 1:0, and treat with ultrasonic power of 40W for 20 min to obtain intrinsic graphene mixed solution.

[0059] Step 2: The intrinsic graphene mixed solution was sheared at 800 rpm for 22 min to obtain an intrinsic graphene aqueous solution;

[0060] Step 3: Add sodium riboflavin to the intrinsic graphene aqueous solution at a mass ratio of 15:1 (intrinsic graphene to sodium riboflavin phosphate), and sonicate at 40W for 15 minutes to obtain intrinsic graphene hydrogel.

[0061] Step 4: Place the intrinsic graphene hydrogel in a freezing mold, and then freeze the mold at -20°C for 720 minutes to obtain intrinsic graphene hydrogel ice crystals. Dry the intrinsic graphene hydrogel ice crystals for 36 hours to obtain an intrinsic graphene preform. The prepared intrinsic graphene preform exhibits wave transmission properties, with an X-band electromagnetic wave transmittance of ~98%.

[0062] Example 2

[0063] The difference from Example 1 is that the concentration of the intrinsic graphene dispersion in step 1 is 10 mg / ml, and the mass ratio of intrinsic graphene to polyvinyl alcohol is 10:1. In step 4, the mold is placed in a freezing container and frozen at -100°C for 360 min. The prepared intrinsic graphene preform has wave transmission properties, with an X-band electromagnetic wave transmittance of ~97%.

[0064] Example 3

[0065] The difference from Example 1 is that the concentration of the intrinsic graphene dispersion in step 1 is 15 mg / ml, and the mass ratio of intrinsic graphene to polyvinyl alcohol is 12:1. In step 4, the mold is placed in a freezing container and frozen at -180°C for 10 min. The prepared intrinsic graphene preform has wave transmission properties, with an X-band electromagnetic wave transmittance of ~92%.

[0066] Example 4

[0067] This embodiment describes a method for preparing an intrinsic graphene preform with tunable electromagnetic properties. The specific steps are as follows:

[0068] Step 1: Take 10 mg / ml of intrinsic graphene dispersion, add sodium carboxymethyl cellulose and sodium dodecyl sulfate to the intrinsic graphene dispersion at a mass ratio of 10:1 for intrinsic graphene and 1:3 for intrinsic graphene and sodium dodecyl sulfate, and treat with ultrasonic power of 120 W for 12 min to obtain intrinsic graphene mixed solution;

[0069] Step 2: The intrinsic graphene mixed solution was sheared at 1700 rpm for 12 min to obtain an intrinsic graphene aqueous solution;

[0070] Step 3: Add sodium riboflavin phosphate to the intrinsic graphene aqueous solution at a mass ratio of 27:1 (intrinsic graphene to sodium riboflavin phosphate), and sonicate at 120W for 9 minutes to obtain intrinsic graphene hydrogel.

[0071] Step 4: Place the intrinsic graphene hydrogel in a freezing mold, and then freeze the mold at -180°C for 10 minutes to obtain intrinsic graphene hydrogel ice crystals. Dry the intrinsic graphene hydrogel ice crystals for 42 hours to obtain an intrinsic graphene preform. The prepared intrinsic graphene preform exhibits microwave absorption properties, with a minimum reflection loss of -50.7 dB for X-band electromagnetic wave absorption.

[0072] Example 5

[0073] The difference from Example 4 is that in step 1, the mass ratio of intrinsic graphene to sodium dodecyl sulfate is 1:5. In step 4, the mold is placed in a freezing container and frozen at -20°C for 720 minutes. The prepared intrinsic graphene preform has microwave absorption properties, with a minimum reflection loss of -10.6 dB for X-band electromagnetic wave absorption.

[0074] Example 6

[0075] This embodiment describes a method for preparing an intrinsic graphene preform with tunable electromagnetic properties. The specific steps are as follows:

[0076] Step 1: Take 10 mg / ml of intrinsic graphene dispersion, add sodium carboxymethyl cellulose and polystyrene to the intrinsic graphene dispersion according to the intrinsic graphene to sodium carboxymethyl cellulose mass ratio of 16:1 and the intrinsic graphene to polystyrene mass ratio of 1:8, and treat with ultrasonic power of 200W for 3 min to obtain intrinsic graphene mixed solution.

[0077] Step 2: The intrinsic graphene mixed solution was sheared at 2600 rpm for 2 min to obtain an intrinsic graphene aqueous solution;

[0078] Step 3: Add sodium riboflavin phosphate to the intrinsic graphene aqueous solution at a mass ratio of 40:1 (intrinsic graphene to sodium dodecylbenzene sulfonate), and sonicate at 200W for 3 minutes to obtain intrinsic graphene hydrogel.

[0079] Step 4: Place the intrinsic graphene hydrogel in a freezing mold, and freeze the mold at -20°C for 720 min to obtain intrinsic graphene hydrogel ice crystals. Dry the intrinsic graphene hydrogel ice crystals for 48 h to obtain the intrinsic graphene preform. The prepared intrinsic graphene preform exhibits electromagnetic shielding properties, with a total shielding effectiveness of ~45.34 dB in the X-band, a reflection effectiveness of ~5.88 dB, and a reflection effectiveness of ~39.46 dB.

[0080] Example 7

[0081] The difference from Example 6 is that in step 4, the mold is placed in a freezing container and frozen at -180°C for 10 minutes. The prepared intrinsic graphene preform has electromagnetic shielding properties, with a total shielding effectiveness of ~44.95dB in the X-band, a reflection effectiveness of ~4.40dB, and a reflection effectiveness of ~40.55dB.

[0082] like Figure 1 As shown in Figure (a), the intrinsic graphene preform prepared in Example 1 shows that the intrinsic graphene without pore-forming agent and frozen at a higher temperature tends to stack into large sheets due to interlayer van der Waals forces, without forming a connected network structure, which is conducive to the construction of intrinsic graphene wave-transparent materials. Figure (b) shows the intrinsic graphene preform prepared in Example 3, showing that by increasing the intrinsic graphene content and lowering the freezing temperature of the intrinsic graphene hydrogel, the intrinsic graphene without pore-forming agent can achieve directional alignment. Figure (c) shows the intrinsic graphene preform prepared in Example 4, showing that the addition of a small amount of pore-forming agent can make the directional alignment of the intrinsic graphene pores more uniform and regular, and wrinkles appear on the surface of the large sheets. The uniformly oriented pores can regulate the impedance matching between the material and free space, which is conducive to the formation of intrinsic graphene wave-absorbing materials. As shown in Figure (d), the intrinsic graphene preform prepared in Example 6 demonstrates that increasing the content of the pore-forming agent and freezing the intrinsic graphene sheets at a higher temperature can assemble them into a three-dimensional network structure, which helps to form an intrinsic graphene electromagnetic shielding material.

[0083] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing an intrinsic graphene preform with tunable electromagnetic properties in the X-band, characterized in that, Includes the following steps: S1: Take raw graphite powder and use liquid phase exfoliation method to perform multiple ultrasonic exfoliations to obtain intrinsic graphene water-based suspension; take the supernatant of intrinsic graphene water-based suspension and use rotary evaporation method to prepare intrinsic graphene dispersion. S2: Add gelling agent and pore-forming agent to intrinsic graphene dispersion, and perform ultrasonic treatment to obtain intrinsic graphene mixed solution; S3: Shear the intrinsic graphene mixture to obtain an intrinsic graphene aqueous solution; S4: Add a foam stabilizer to an intrinsic graphene aqueous solution and perform ultrasonic treatment to obtain an intrinsic graphene hydrogel. S5: Freeze the intrinsic graphene hydrogel to obtain intrinsic graphene hydrogel ice crystals, and dry the intrinsic graphene hydrogel ice crystals to obtain an intrinsic graphene preform.

2. The method for preparing an intrinsic graphene preform with tunable X-band electromagnetic properties according to claim 1, characterized in that, In step S1, the concentration of the intrinsic graphene dispersion is 5~15 mg / ml.

3. The method for preparing an intrinsic graphene preform with tunable X-band electromagnetic properties according to claim 1, characterized in that, In step S1, the mass ratio of graphene to raw graphite powder in the supernatant of the intrinsic graphene aqueous suspension is 1:8~14.

4. The method for preparing an intrinsic graphene preform with tunable X-band electromagnetic properties according to claim 1, characterized in that, In S1, the intrinsic graphene in the intrinsic graphene dispersion has a sheet size of 5~15 μm and a thickness of 0.5~1.5 nm, with a Raman defect degree of... I D / I G The value is 0.1~0.4; The viscosity of the supernatant is 1.30~1.52 cP, and the surface tension is 65~68 mN / m.

5. The method for preparing an intrinsic graphene preform with tunable X-band electromagnetic properties according to claim 1, characterized in that, In step S2, the gelling agent is polyvinyl alcohol or sodium carboxymethyl cellulose, and the mass ratio of intrinsic graphene to gelling agent in the intrinsic graphene mixed solution is 4~16:

1.

6. The method for preparing an intrinsic graphene preform with tunable X-band electromagnetic properties according to claim 1, characterized in that, In step S2, the pore-forming agent is sodium dodecyl sulfate or polystyrene.

7. The method for preparing an intrinsic graphene preform with tunable X-band electromagnetic properties according to claim 1, characterized in that, In step S3, the rotational speed of the shearing process is 800~2600 rpm, and the shearing time is 2~22 min.

8. The method for preparing an intrinsic graphene preform with tunable X-band electromagnetic properties according to claim 1, characterized in that, In step S4, the foam stabilizer is one or more of sodium riboflavin phosphate and sodium dodecylbenzene sulfonate, and the mass ratio of intrinsic graphene to foam stabilizer in the intrinsic graphene hydrogel is 15~40:

1.

9. The method for preparing an intrinsic graphene preform with tunable X-band electromagnetic properties according to claim 1, characterized in that, In step S5, the freezing temperature is -180 to -20 °C, the freezing time is 10 to 720 min, and the drying time is 36 to 48 h.

10. An intrinsic graphene preform prepared by a method for preparing an intrinsic graphene preform with tunable X-band electromagnetic properties according to any one of claims 1 to 9.

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