CN113148996B - Three-dimensional porous graphene aerogel wave-absorbing material and preparation method thereof - Google Patents
Three-dimensional porous graphene aerogel wave-absorbing material and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a three-dimensional porous graphene aerogel wave-absorbing material and a preparation method thereof, wherein the method comprises the following steps: respectively measuring a graphene oxide aqueous solution, a reducing agent and an antifreeze agent, and obtaining a mixed solution after magnetic stirring and ultrasonic dispersion; transferring the mixed solution into a glass bottle, sealing and placing the glass bottle in an oven for pre-reduction to obtain pre-reduced graphene hydrogel; freezing the pre-reduced graphene hydrogel, and then thawing at room temperature to obtain the pre-reduced graphene hydrogel after freeze thawing; sealing the pre-reduced graphene hydrogel subjected to freeze thawing, placing the pre-reduced graphene hydrogel in an oven for continuous reduction to obtain graphene hydrogel; and (3) putting the graphene hydrogel into an ethanol/water mixed solution for aging, and freeze-drying to obtain the three-dimensional graphene oxide aerogel. The aperture size and the volume of the three-dimensional graphene wave-absorbing material can be freely controlled, and the free design of different electromagnetic wave absorption can be realized by controlling the aperture size and the volume of the wave-absorbing material.
Description
Technical Field
The invention relates to the field of wave-absorbing material preparation, in particular to a three-dimensional porous graphene aerogel wave-absorbing material and a preparation method thereof.
Background
With the rapid development of electronic technology, technologies such as television broadcasting communication, microwave darkroom, radar guidance and the like are popularized and applied, and a novel wave-absorbing material serving as one of the first-selected effective means for reducing electromagnetic radiation becomes a research hotspot in recent years. The requirements of the absorbing material in both military field and civil field are continuously increased, and more attention is paid to the application research of the absorbing material. As a novel carbon material, the graphene has special structure and performance, can meet the requirements of thin, wide, light and strong of a novel wave-absorbing material, and has good application prospect in the field of microwave absorption.
The three-dimensional graphene aerogel absorbs electromagnetic waves, and is related to the carbon material of the aerogel on the one hand; on the other hand, the porous structure absorbs the electromagnetic wave by reflecting, scattering and interfering the electromagnetic wave, wherein the size and distribution of the pore diameter have a great influence on the absorption of the electromagnetic wave. However, the three-dimensional graphene prepared by the prior art has the problems that the pore size is not easy to control and the pore size distribution is not uniform, so that the electromagnetic wave absorption performance of the three-dimensional graphene material is not ideal. At present, researchers mainly improve the wave-absorbing performance of the graphene aerogel by doping heteroatoms or introducing second-phase substances (dielectric materials, magnetic materials and the like), but the above strategy can cause the problems of increased density of the wave-absorbing material, increased filling amount, complex preparation process, intrinsic flexible elasticity attenuation of the graphene aerogel and the like. The invention aims to improve the existing preparation method of the graphene aerogel and regulate and control the pore structure of the graphene aerogel, so that the wave-absorbing performance of the graphene aerogel is improved.
Disclosure of Invention
In order to solve the problems, the invention provides a three-dimensional porous graphene aerogel wave-absorbing material and a preparation method thereof. The aperture size and the volume of the three-dimensional graphene wave-absorbing material can be freely controlled, and the free design of different electromagnetic wave absorption can be realized by controlling the aperture size and the volume of the wave-absorbing material.
The technical scheme of the invention is as follows: a preparation method of a three-dimensional porous graphene aerogel wave-absorbing material comprises the following steps:
(1) respectively measuring a graphene oxide aqueous solution, a reducing agent and an antifreeze agent, and obtaining a mixed solution after magnetic stirring and ultrasonic dispersion;
(2) transferring the mixed solution prepared in the step (1) into a glass bottle, sealing and placing in an oven for pre-reduction to obtain pre-reduced graphene hydrogel;
(3) freezing the pre-reduced graphene hydrogel obtained in the step (2) at-30 to-70 ℃ for 10-60 min, and then thawing for 30-60 min at room temperature to obtain the pre-reduced graphene hydrogel after freeze thawing;
(4) sealing the pre-reduced graphene hydrogel obtained in the step (3) after freeze thawing, placing the pre-reduced graphene hydrogel in an oven for continuous reduction to obtain graphene hydrogel;
(5) and (5) placing the graphene hydrogel obtained in the step (4) into an ethanol/water mixed solution, aging for 24-72 hours, and freeze-drying to obtain the three-dimensional graphene oxide aerogel.
Further, the concentration of the graphene oxide aqueous solution in the step (1) is 1-5 mg/ml; the reducing agent is at least one of ascorbic acid, hydroiodic acid, sodium bisulfite, ethylenediamine, pyrrole, aniline and dopamine; the antifreeze is at least one of methanol, ethanol and isopropanol; the mass ratio of the graphene oxide to the reducing agent is 1: 1-5; the volume ratio of the graphene oxide aqueous solution to the antifreeze agent is 1: 0.01 to 0.1.
Further, the pre-reduction temperature in the step (2) is 50-95 ℃, and the time is 15-120 min.
Further, the continuous reduction temperature in the step (4) is 70-95 ℃, and the time is 4-10 h.
Further, the volume ratio of ethanol to water in the ethanol/water mixed solution is 1: 4-1: 6.
the invention also provides the three-dimensional porous graphene aerogel wave-absorbing material prepared by the method, wherein the density of the graphene aerogel is 2-10 mg/cm 3 The porosity is 85-97%, the filling amount of the graphene aerogel is 0.2-1.5 wt%, and the effective absorption RL of the ultra-wide band of 6-18 GHz is less than-10 dB.
Has the advantages that: the method provided by the invention is simple in process and low in cost, and the prepared three-dimensional porous graphene aerogel has the characteristics of ultralow density, adjustable pore structure, ultralow filling amount, effective absorption of an ultra-wide band and the like. The three-dimensional porous graphene aerogel prepared by controlling different pre-reduction times can realize free design of different electromagnetic wave absorption. The three-dimensional porous graphene aerogel prepared by the invention can realize effective absorption (RL is less than-10 dB) of an ultra-wide band (6-18 GHz).
Drawings
FIG. 1 is a physical diagram of three-dimensional graphene aerogel prepared in examples 1 to 3;
fig. 2 is a scanning electron microscope image of the three-dimensional porous graphene aerogel prepared in examples 1 to 3, wherein a is sample 1, b is sample 2, and c is sample 3;
FIG. 3 is real parts of dielectric constants of three-dimensional porous graphene aerogels prepared in examples 1 to 3 (different pre-reduction times);
fig. 4 shows the wave-absorbing properties of the three-dimensional porous graphene aerogels (with different pre-reduction times) prepared in examples 1 to 3.
Fig. 5 is a pore size distribution diagram of three-dimensional porous graphene aerogels (different pre-reduction times) prepared in examples 1 to 3.
Detailed description of the invention
The technical solution of the present invention is further explained below with reference to specific embodiments.
Example 1
Graphene oxide aqueous solution (3 mg/mL, 2 mL), ascorbic acid (18 mg) and ethanol (20 mL) were weighed, magnetically stirred, and ultrasonically dispersed in cold water to obtain a mixed solution. And transferring the mixed solution into a glass bottle, sealing, and pre-reducing in a 50 ℃ oven for 15min to obtain the pre-reduced graphene hydrogel. Freezing the pre-reduced graphene hydrogel at-30 ℃ for 60 min, and then thawing the pre-reduced graphene hydrogel at room temperature for 30 min to obtain the pre-reduced graphene hydrogel after freeze thawing. And (3) sealing the pre-reduced graphene hydrogel after freeze thawing, placing the pre-reduced graphene hydrogel in an oven at 95 ℃ for continuous reduction for 4 hours to obtain the graphene hydrogel. And (3) putting the hydrogel into an ethanol/water mixed solution (the volume ratio of ethanol to water is 1: 4), aging for 24 h, freezing for 12 h at-60 ℃, taking out, putting into a freeze drying device, and drying for 24 h to obtain the three-dimensional graphene aerogel (sample 1). The density of the prepared graphene aerogel is 3.10mg/cm 3 The filling amount is 0.2 wt%, the porosity is 97%, and effective absorption (RL < -10 dB) in a frequency band (6-11 GHz) can be realized. The sample diagram is shown in FIG. 1, and the real part of the dielectric constant of the sample 1 reaches 5, as shown in FIG. 3; the minimum reflection loss reaches-27.1 dB, and the effective absorption bandwidth reaches 6.35GHz, as shown in FIG. 4; the pore size distribution of the graphene aerogel is concentrated in the range around 117 microns, as shown in fig. 5.
Example 2
Graphene oxide aqueous solution (5 mg/mL, 2 mL), sodium bisulfite (10 mg) and methanol (200 mL) were weighed, magnetically stirred, and ultrasonically dispersed in cold water to obtain a mixed solution. Transferring the mixed solution to a glass bottleSealing, and pre-reducing in an oven at 80 ℃ for 120min to obtain the pre-reduced graphene hydrogel. Freezing the pre-reduced graphene hydrogel at-50 ℃ for 45 min, and then thawing for 45 min at room temperature to obtain the pre-reduced graphene hydrogel after freeze thawing. And (3) sealing the pre-reduced graphene hydrogel after freeze thawing, placing the pre-reduced graphene hydrogel in an oven at 80 ℃ for continuous reduction for 8 hours to obtain the graphene hydrogel. And (3) putting the hydrogel into an ethanol/water mixed solution (the volume ratio of ethanol to water is 1: 5), aging for 48 h, freezing for 12 h at-60 ℃, taking out, putting into a freeze drying device, and drying for 24 h to obtain the three-dimensional graphene aerogel (sample 2). The density of the prepared graphene aerogel is 5.80 mg/cm 3 The filling amount is 0.75wt%, the porosity is 91%, and effective absorption (RL < -10 dB) in a frequency band (10-18 GHz) can be realized. The sample diagram is shown in FIG. 1, and the real part of the dielectric constant of sample 2 reaches 6.3, as shown in FIG. 3; the minimum reflection loss reaches-61.6 dB, and the effective absorption bandwidth reaches 7.75GHz, as shown in FIG. 4; the pore size distribution of the graphene aerogel is concentrated in the range around 72 microns, as shown in fig. 5.
Example 3
Graphene oxide aqueous solution (1 mg/mL, 2 mL), hydroiodic acid (10 mg) and isopropanol (100 mL) were measured, and a mixed solution was obtained by magnetic stirring and ultrasonic dispersion in cold water. And transferring the mixed solution into a glass bottle, sealing, and pre-reducing in an oven at 95 ℃ for 60 min to obtain the pre-reduced graphene hydrogel. Freezing the pre-reduced graphene hydrogel at-70 ℃ for 10 min, and then thawing the pre-reduced graphene hydrogel at room temperature for 60 min to obtain the pre-reduced graphene hydrogel after freeze thawing. And sealing the pre-reduced graphene hydrogel after freeze thawing, placing the pre-reduced graphene hydrogel in an oven at 70 ℃ for continuous reduction for 10 hours to obtain the graphene hydrogel. And (3) putting the hydrogel into an ethanol/water mixed solution (the volume ratio of ethanol to water is 1: 6), aging for 72 h, freezing for 12 h at-60 ℃, taking out, putting into a freeze drying device, and drying for 24 h to obtain the three-dimensional graphene aerogel (sample 3). The density of the prepared graphene aerogel is 8.50mg/cm 3 The filling amount is 1.5wt%, the porosity is 85%, and effective absorption (RL < -10 dB) in a frequency band (13-18 GHz) can be realized. The sample diagram is shown in FIG. 1, and the real part of the dielectric constant of sample 3 is expressedTo 8.8, as shown in FIG. 3; the minimum reflection loss reaches-14.6 dB, and the effective absorption bandwidth reaches 7.68GHz, as shown in FIG. 4; the pore size distribution of the graphene aerogel is concentrated in the range of about 51 microns, as shown in fig. 5.
Fig. 2 is scanning electron microscope pictures of the graphene aerogels prepared in the above examples 1 to 3, all of which show a three-dimensional connected porous structure. Fig. 3, 4 and 5 show the electromagnetic parameters, the wave-absorbing properties and the pore size distribution of the three-dimensional porous graphene aerogel (samples 1 to 3), respectively. From sample 1 to sample 3, the pore structure becomes smaller as the degree of shrinkage increases. The real part of the dielectric constant is gradually increased (figure 3), and the corresponding wave-absorbing performance shows the trend of increasing first and then decreasing (figure 4). The pore size distribution of the graphene aerogel can be obtained by mercury intrusion test (fig. 5), and the peak of the curve corresponds to the most probable pore in each sample. The corresponding pore size was seen to decrease gradually from sample 1 to sample 3.
Claims (4)
1. A preparation method of a three-dimensional porous graphene aerogel wave-absorbing material is characterized by comprising the following steps:
(1) respectively measuring a graphene oxide aqueous solution, a reducing agent and an antifreeze agent, and obtaining a mixed solution after magnetic stirring and ultrasonic dispersion;
(2) transferring the mixed solution prepared in the step (1) into a glass bottle, sealing and placing the glass bottle in an oven, and pre-reducing the mixed solution at 50-95 ℃ for 15-120 min to obtain pre-reduced graphene hydrogel;
(3) freezing the pre-reduced graphene hydrogel obtained in the step (2) at-30 to-70 ℃ for 10-60 min, and then thawing for 30-60 min at room temperature to obtain the pre-reduced graphene hydrogel after freeze thawing;
(4) sealing the pre-reduced graphene hydrogel obtained in the step (3) after freeze thawing, placing the pre-reduced graphene hydrogel in an oven for continuous reduction, wherein the continuous reduction temperature is 70-95 ℃ and the time is 4-10 hours, so as to obtain the graphene hydrogel;
(5) and (5) placing the graphene hydrogel obtained in the step (4) into an ethanol/water mixed solution, aging for 24-72 hours, and freeze-drying to obtain the three-dimensional graphene oxide aerogel.
2. The preparation method of the three-dimensional porous graphene aerogel wave-absorbing material according to claim 1, wherein the concentration of the graphene oxide aqueous solution in the step (1) is 1-5 mg/ml; the reducing agent is at least one of ascorbic acid, hydroiodic acid, sodium bisulfite, ethylenediamine, pyrrole, aniline and dopamine; the antifreeze agent is at least one of methanol, ethanol and isopropanol; the mass ratio of the graphene oxide to the reducing agent is 1: 1-5; the volume ratio of the graphene oxide aqueous solution to the antifreeze agent is 1: 0.01 to 0.1.
3. The preparation method of the three-dimensional porous graphene aerogel wave-absorbing material according to claim 1, wherein the volume ratio of ethanol to water in the ethanol/water mixed solution is 1: 4-6.
4. The three-dimensional porous graphene aerogel wave-absorbing material prepared by the method according to any one of claims 1 to 3, wherein the density of the graphene aerogel is 2-10 mg/cm 3 The porosity is 85-97%, the filling amount of the graphene aerogel is 0.2-1.5 wt%, and the effective absorption RL of the ultra-wide band of 6-18 GHz is less than-10 dB.
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