CN109592964B - Elasticity-controllable graphene aerogel for electromagnetic shielding and preparation method thereof - Google Patents
Elasticity-controllable graphene aerogel for electromagnetic shielding and preparation method thereof Download PDFInfo
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Abstract
The invention provides a preparation method of elasticity-controllable graphene aerogel for electromagnetic shielding, which comprises the following steps: firstly, adding a silver nanowire aqueous dispersion into a graphene oxide aqueous dispersion under a stirring condition, and stirring for 5-60 min to obtain a graphene oxide/silver nanowire aqueous dispersion; adding a reducing agent into the obtained graphene oxide/silver nanowire water dispersion, and stirring until the reducing agent is dissolved to obtain a mixed solution; then heating the obtained mixed solution at 50-100 ℃ for 30-90 min to obtain hydrogel I; freezing the obtained hydrogel I at the temperature of between 40 ℃ below zero and 10 ℃ below zero for 0.5 to 8 hours, and then thawing the hydrogel I at room temperature to obtain a hydrogel II; heating the obtained hydrogel II at 70-100 ℃ for 2-8 h to obtain hydrogel III; and washing the obtained hydrogel III, and drying at normal pressure to obtain the graphene aerogel. The graphene aerogel prepared by the method has high electromagnetic shielding efficiency in unit density.
Description
Technical Field
The invention relates to the technical field of new material preparation, and particularly relates to an elastic controllable graphene aerogel for electromagnetic shielding and a preparation method thereof.
Background
With the continuous development of the information age and the wide popularization of high-performance electronic products and radio technologies, electromagnetic wave pollution becomes a considerable problem in the life of people. The 5G era is approaching gradually, and along with the introduction of high frequency, the upgrade of parts and the multiplication of the number of networking equipment and antennas, the electromagnetic interference and radiation between the equipment and the equipment are ubiquitous, so that the service performance and the service life of the equipment and surrounding equipment are influenced, and certain harm is caused to the physical health of people. There is a continuing need for high performance electromagnetic shielding devices. The conductivity is a key factor affecting the electromagnetic shielding material, and the electromagnetic shielding products on the market at present are mainly metal-based materials with good performance, but the high density and poor environmental stability seriously limit the further development thereof. Therefore, in addition to good electromagnetic shielding performance, light weight and excellent chemical stability are also important factors for determining the development of electromagnetic shielding products.
The carbon material, especially the three-dimensional carbon material constructed by graphene and carbon nano tubes has a wide application prospect in the aspect of resisting electromagnetic radiation and interference due to the characteristics of ultralow density, excellent conductivity, chemical stability, corrosion resistance and the like. At present, chemical or thermal reduction of graphene oxide is a common method for preparing graphene aerogel, and the method has the characteristics of simplicity, low cost and the like, but the conductivity of the chemically or thermally reduced graphene is greatly reduced, which is not beneficial to the application of the graphene in the field of electromagnetic shielding, so that a second component is usually added to improve the conductivity of the material. The silver nanowires have high conductivity, and the large length-diameter ratio of the silver nanowires is convenient for being interwoven with one another to form a passage, but the silver nanowires alone are easy to corrode when exposed to the environment, so that the performance of the material is influenced.
The Chinese invention patent with the application number of 201510455638.9 prepares silver nanowire/graphene composite elastic aerogel, the aerogel has the characteristics of high elasticity, adjustable resistance and the like, but firstly, a drying mode with high energy consumption is involved in the preparation process of the aerogel, and meanwhile, the graphene aerogel prepared by adopting freeze drying or supercritical drying has small aperture and thin hole wall, is not enough to resist large external force deformation and has poor rebound resilience. The Chinese patent with application number 201810101813.8 prepares a silicone rubber/graphene/silver nanowire nano composite three-dimensional porous material for electromagnetic shielding, the material has high conductivity and outstanding electromagnetic shielding performance, but the material also relates to a drying mode with high energy consumption and time consumption in the preparation process, and the obtained aerogel has smaller aperture, thinner pore wall and poorer elasticity. The preparation method has the disadvantages of complicated process, time and energy consumption, narrow application range and no contribution to large-scale application of materials. The light and flexible graphene composite material is prepared by the Chinese patent with the application number of 201410692427.2, and has high-efficiency electromagnetic shielding effectiveness, and the unit density electromagnetic shielding effectiveness can reach 800 dB-cm 3/g. However, the polymer foam template selected by adopting a similar method needs to have a macroporous structure, has no universality on the absorption degree of graphene or precursors with different sizes, and is easy to generate gradient distribution in the process of immersing in a graphene solution, so that the performance is influenced by uneven distribution. In addition, the conducting network formed by adopting a similar method has the advantages that the framework does not have a good protection effect on the filler, and the performance of the material is directly influenced. The Chinese invention patent with the application number of 201610566686.X adopts a normal pressure drying method to prepare the strength-controllable amphiphilic graphene aerogel, and realizes the regulation and control of the aerogel strength by controlling the content of the cellulose nanocrystal. So far, no report is available on the research of preparing graphene/silver nanowire aerogel with uniform structure and controllable elasticity by directly utilizing graphene oxide and silver nanowire dispersion liquid and a simple normal-pressure drying method.
In view of the above, there is a need for improvements in the prior art.
Disclosure of Invention
The invention aims to provide a graphene aerogel which is low in energy consumption, has an electromagnetic shielding function and is controllable in elasticity and a preparation method thereof;
in order to solve the technical problems, the invention provides a preparation method of an elastic controllable graphene aerogel for electromagnetic shielding, which comprises the following steps of:
s1, preparing a graphene oxide/silver nanowire water dispersion:
adding the silver nanowire aqueous dispersion into the graphene oxide aqueous dispersion under a stirring condition (the stirring speed is 800-1500 rpm), and stirring for 5-60 min to obtain the graphene oxide/silver nanowire aqueous dispersion (the graphene oxide/silver nanowire aqueous dispersion is uniformly and stably dispersed);
adding a reducing agent into the obtained graphene oxide/silver nanowire water dispersion, and stirring (at the stirring speed of 800-1500 rpm) until the reducing agent is dissolved to obtain a mixed solution;
s2, preparing graphene aerogel:
2.1, heating the obtained mixed solution at 50-100 ℃ for 30-90 min to obtain hydrogel I (suspended in water);
2.2, freezing the obtained hydrogel I at the temperature of between 40 ℃ below zero and 10 ℃ below zero for 0.5 to 8 hours, and then melting the hydrogel I at room temperature (20 to 35 ℃) to obtain hydrogel II;
2.3, heating the obtained hydrogel II at the temperature of 70-100 ℃ for 2-8 h to obtain hydrogel III;
and 2.4, washing the obtained hydrogel III (removing unreacted reducing agent and other impurities), and drying the hydrogel III under normal pressure (namely one atmosphere) to constant weight to obtain the graphene aerogel.
Note: the drying temperature can be selected according to actual conditions, and if the solvent used for washing is water, the drying can be carried out at 10-100 ℃.
The improvement of the preparation method of the elasticity-controllable graphene aerogel for electromagnetic shielding is as follows:
the volume ratio of the silver nanowire aqueous dispersion to the graphene oxide aqueous dispersion is 1: 0.8-1.2 (optimally 1: 1).
The preparation method of the elasticity-controllable graphene aerogel for electromagnetic shielding is further improved as follows:
the concentration of the graphene oxide aqueous dispersion is 0.5-15 mg/mL, and the size of the used graphene oxide is 0.5-70 mu m;
the concentration of the silver nanowire aqueous dispersion is 0.1-15 mg/mL, the diameter of the used silver nanowire is 5-200 nm, and the length of the silver nanowire aqueous dispersion is 1-100 mu m.
The preparation method of the elasticity-controllable graphene aerogel for electromagnetic shielding is further improved as follows:
the mass ratio of the reducing agent to the graphene oxide is 1.5-2.5: 1 (most preferably 2: 1);
the mixture was heated at 60 ℃ for 40min to obtain hydrogel i (suspended in water).
The preparation method of the elasticity-controllable graphene aerogel for electromagnetic shielding is further improved as follows:
and freezing the obtained hydrogel I at the temperature of-20 ℃ for 2 hours, and then thawing at room temperature (20-35 ℃) to obtain a hydrogel II.
The preparation method of the elasticity-controllable graphene aerogel for electromagnetic shielding is further improved as follows:
the hydrogel II thus obtained was heated at 90 ℃ for 6 hours to give a hydrogel III.
The preparation method of the elasticity-controllable graphene aerogel for electromagnetic shielding is further improved as follows:
the reducing agent is at least one of hydrazine hydrate, hydroiodic acid, ascorbic acid, glucose, tannic acid and tea polyphenol.
The preparation method of the elasticity-controllable graphene aerogel for electromagnetic shielding is further improved as follows:
in step 2.4, the hydrogel III is washed with water, methanol or ethanol.
In order to solve the technical problems, the invention further provides the elastic controllable graphene aerogel for electromagnetic shielding, which is prepared by the method.
As an improvement of the elasticity-controllable graphene aerogel for electromagnetic shielding, the invention comprises the following steps:
the elastic controllable graphene aerogel for electromagnetic shielding comprises the following components in percentage by mass:
30 to 99.5 percent of graphene
0.5 to 70 percent of silver nanowire
The elastic controllable graphene aerogel for electromagnetic shielding has electromagnetic shielding effectiveness of 20-80 dB.
Aiming at the prior art, the invention has the technical advantages that:
(1) the graphene aerogel with excellent electromagnetic shielding performance is prepared in a simple and low-energy-consumption mode, so that the production cost is greatly reduced;
(2) the graphene aerogel obtained by the invention has ultralow density (lower than 20mg/cm3), so that the prepared aerogel has high electromagnetic shielding efficiency in unit density;
(3) due to the good combination between the silver nanowires and the graphene, the silver nanowires can be protected by the graphene sheet layer from oxidation and corrosion caused by exposure to the external environment, so that the service life of the material is prolonged;
(4) the rebound resilience of the graphene aerogel can be regulated and controlled by changing the content of the silver nanowires, and the graphene aerogel has an optimal value (the energy loss coefficient is 0.43).
Drawings
The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.
Fig. 1 is an SEM image of the graphene aerogel obtained in example 1 (the left image is a micro-topography image of the obtained graphene aerogel, and the right image is a morphological schematic diagram of silver nanowires in the obtained graphene aerogel);
fig. 2 is a physical diagram of the graphene aerogel obtained in example 1 during a compression process (the left diagram is a state diagram of the uncompressed graphene aerogel, the middle diagram is a state diagram of the left diagram when the graphene aerogel is compressed, and the right diagram is a state diagram of the middle diagram after the graphene aerogel is decompressed);
fig. 3 shows the electromagnetic shielding effectiveness of the graphene aerogel obtained in example 4 at 8.2-12.4 GHz.
Note: SEM, scanning electron microscope.
Detailed Description
The invention will be further described with reference to specific examples, but the scope of the invention is not limited thereto.
Embodiment 1, a method for preparing an elasticity-controllable graphene aerogel for electromagnetic shielding, comprising the following steps performed in sequence:
1. preparing raw materials:
graphene oxide aqueous dispersion: the concentration is 10mg/mL, and the size of the used graphene oxide is 5 μm;
silver nanowire aqueous dispersion: the concentration is 1mg/mL, and the diameter of the silver nanowire is 60nm, and the length of the silver nanowire is 10 μm.
2. Preparing a graphene oxide/silver nanowire aqueous dispersion:
slowly adding the silver nanowire aqueous dispersion into the graphene oxide aqueous dispersion under the stirring condition (the stirring speed is 800rpm), continuously stirring for 10min to obtain the graphene oxide/silver nanowire aqueous dispersion which is uniformly and stably dispersed, then adding ascorbic acid serving as a reducing agent, and stirring (the stirring speed is 800rpm) until the ascorbic acid is dissolved to obtain a mixed solution;
the volume ratio of the graphene oxide aqueous dispersion to the silver nanowire aqueous dispersion is 1: 1;
the mass ratio of the ascorbic acid to the graphene oxide is 2: 1.
note: the reducing agent is at least one of hydrazine hydrate, hydroiodic acid, ascorbic acid, glucose, tannin and tea polyphenols
3. Preparing graphene aerogel:
3.1, placing the obtained mixed solution in an oven at 60 ℃ and heating for 40min to obtain hydrogel I (suspended in water);
3.2, freezing the obtained hydrogel I at the temperature of-20 ℃ for 2h, and then thawing at room temperature (25 ℃) to obtain hydrogel II.
3.3, heating the obtained hydrogel II at 90 ℃ for 6h to obtain hydrogel III.
And 3.4, washing the obtained hydrogel III by using water, removing unreacted ascorbic acid and other impurities, and drying at 60 ℃ under normal pressure (namely one atmosphere) to obtain the graphene aerogel.
Note: the hydrogel III may also be washed with methanol or ethanol.
The graphene content of the obtained graphene aerogel is 90.1%, and the silver nanowire content is 9.9%;
note: the above% is by mass.
The electron microscope picture of the obtained graphene aerogel is shown in figure 1, and the structural characteristics of the graphene aerogel are as follows: the three-dimensional structural unit has a porous structure formed by mutually overlapping graphene sheets, and silver nanowires are attached between the graphene sheets forming the pore walls or on the surfaces of the graphene sheets, so that the three-dimensional structural unit is formed.
The density of the obtained graphene aerogel is 7.31mg/cm3The electromagnetic shielding effectiveness is 21dB, and the unit density electromagnetic shielding effectiveness is 2873dB cm3·g-1The energy loss coefficient from the compression curve after compression was 0.52.
Note: the electromagnetic shielding effectiveness is obtained by measuring with a vector network analyzer, the electromagnetic shielding effectiveness per unit density is calculated by dividing the electromagnetic shielding effectiveness by the density, and the energy loss coefficient is obtained according to a compression recovery curve.
The above are prior arts, and the detailed description of the measurement method is not given.
The state of the obtained graphene aerogel compressed under normal pressure (namely, one atmosphere) is shown in fig. 2, the right graph is a state schematic diagram of the obtained graphene aerogel under normal pressure (namely, one atmosphere), the middle graph is a state schematic diagram of the graphene compressed under the action of external force, and the left graph is a state schematic diagram of the graphene after the action of external force is cancelled.
Therefore, the graphene aerogel prepared by the method has better rebound resilience and can realize multiple compression rebound.
Note: the energy loss coefficient is small, and the rebound resilience is good.
Example 2, the concentration of the silver nanowire aqueous dispersion in the step 1 of the example 1 is changed from 1mg/mL to 3mg/mL, and the rest is the same as the example 1.
The graphene contained in the obtained graphene aerogel is 76.2%, and the silver nanowires contained in the obtained graphene aerogel is 23.8%;
note: the above% is by mass.
The density of the obtained graphene aerogel is 7.46mg/cm3The electromagnetic shielding effectiveness is 25.4dB, and the unit density electromagnetic shielding effectiveness is 3405dB cm3·g-1The energy loss coefficient from the compression curve after compression was 0.49.
Example 3, the concentration of the silver nanowire aqueous dispersion in the step 1 of the example 1 is changed from 1mg/mL to 8mg/mL, and the rest is the same as the example 1.
The content of graphene in the obtained graphene aerogel is 53.6%, and the content of silver nanowires is 46.4%;
note: the above% is by mass.
The density of the obtained graphene aerogel is 12.79mg/cm3The electromagnetic shielding effectiveness is 35.8dB, and the unit density electromagnetic shielding effectiveness is 2799dB cm3·g-1The energy loss coefficient from the compression curve after compression was 0.75.
Example 4, the concentration of the silver nanowire aqueous dispersion in the step 1 of the example 1 is changed from '1 mg/mL' to '15 mg/mL', and the rest is the same as the example 1.
The content of graphene in the obtained graphene aerogel is 38.6%, and the content of silver nanowires is 61.4%;
note: the above% is by mass.
The density of the obtained graphene aerogel is 19.2mg/cm3The electromagnetic shielding effectiveness is 45.2dB, and the unit density electromagnetic shielding effectiveness is 2354dB cm3·g-1The energy loss coefficient from the compression curve after compression was 0.92.
From the above, when the concentration of the silver nanowire dispersion is 3mg/mL, that is, the weight ratio of the silver nanowires to the graphene oxide is 3:10, the energy loss coefficient of the obtained graphene aerogel is the lowest;
when the weight ratio of the silver nanowires to the graphene oxide exceeds 3:10, the energy loss coefficient increases with the increase of the usage amount of the silver nanowires.
When the weight ratio of the silver nanowires to the graphene oxide is lower than 3:10, the energy loss coefficient increases with the decrease of the usage amount of the silver nanowires.
Therefore, the resilience of the obtained graphene aerogel is controlled by changing the content of the silver nanowires.
Example 5, the temperature of heating the mixed liquid obtained in step 3.1 of example 2 was changed from "60 ℃ to" 75 ℃, and the rest was the same as example 2.
The graphene in the obtained graphene aerogel contains 75.9 percent, and the silver nanowires contain 24.1 percent;
note: the above% is by mass.
The density of the obtained graphene aerogel is 7.37mg/cm3The electromagnetic shielding effectiveness is 26.1dB, and the unit density electromagnetic shielding effectiveness is 3541dB cm3·g-1The energy loss coefficient from the compression curve after compression was 0.47.
Example 6, the reducing agent used in step 2 of example 2 is changed from "ascorbic acid" to "composite reducing agent", wherein the mass ratio of the composite reducing agent to graphene oxide is 2:1, the composite reducing agent consists of ascorbic acid and tea polyphenol, wherein the ratio of ascorbic acid: the mass ratio of the tea polyphenol is 1:1, the rest is identical to example 2.
The content of graphene in the obtained graphene aerogel is 74.1%, and the content of silver nanowires is 25.9%;
note: the above% is by mass.
The density of the obtained graphene aerogel is 7.29mg/cm3The electromagnetic shielding effectiveness is 26.4dB, and the unit density electromagnetic shielding effectiveness is 3621dB cm3·g-1The energy loss coefficient from the compression curve after compression was 0.43.
The graphene aerogels obtained in the above embodiments 2 to 6 each have a porous structure formed by overlapping graphene sheets, and silver nanowires are attached between the graphene sheets constituting the pore walls or on the surface thereof, thereby forming three-dimensional structural units.
Considering the electromagnetic shielding performance and resilience of the obtained graphene aerogel comprehensively, the electromagnetic shielding performance of the graphene aerogel prepared in the above embodiment 6 meets the requirements of the present invention, and the electromagnetic shielding performance per unit density and the energy loss coefficient are the best, so the embodiment 6 is the best case.
Comparative example 1, step 3.2 of example 6 was omitted, i.e.the hydrogel I obtained was heated at 90 ℃ for 6h to give hydrogel III, the remainder being equivalent to
Example 6.
The content of graphene in the obtained graphene aerogel is 75.3%, and the content of silver nanowires is 24.7%;
note: the above% is by mass.
The obtained graphene aerogel has the volume seriously shrunk compared with the hydrogel, and the density of the graphene aerogel is 13.4mg/cm3The electromagnetic shielding effectiveness is 26.1dB, and the unit density electromagnetic shielding effectiveness is 1948dB cm3·g-1The energy loss coefficient from the compression curve after compression was 0.76.
Comparative example 2, the atmospheric drying process used in step 3.4 of example 6 was changed to freeze-drying, i.e. the washed hydrogel iii was frozen in a refrigerator at-75 ℃ for 4h, and the product was subsequently dried in a freeze-dryer for 12h, the remainder being identical to example 6.
The graphene contained in the obtained graphene aerogel is 76.1%, and the silver nanowires contained in the obtained graphene aerogel is 23.9%;
note: the above% is by mass.
The density of the obtained graphene aerogel is 7.45mg/cm3The electromagnetic shielding effectiveness is 25.3dB, and the unit density electromagnetic shielding effectiveness is 3396dB cm3·g-1The energy loss coefficient obtained by the compression curve is 0.56, and the method has high energy consumption and long drying time.
Comparative example 3, the normal pressure drying process adopted in step 3.4 of example 6 is changed into supercritical carbon dioxide drying, namely, the washed hydrogel III is repeatedly replaced by ethanol, and then is dried to constant weight by supercritical drying, and the rest is equal to example 6.
The graphene contained in the obtained graphene aerogel is 76.1%, and the silver nanowires contained in the obtained graphene aerogel is 23.9%;
note: the above% is by mass.
The density of the obtained graphene aerogel is 7.43mg/cm3The electromagnetic shielding effectiveness is 25.3dB, and the unit density electromagnetic shielding effectiveness is 3405dB cm3·g-1The energy loss coefficient obtained by a compression curve after compression is 0.57, and the method has high energy consumption and long drying time.
Compared with freeze drying and supercritical drying, the normal pressure drying has the advantages of low energy consumption and short time consumption.
Comparative example 4, the silver nanowires used in step 1 of example 6 were changed to cellulose nanocrystals, and the rest was identical to example 6.
The content of graphene in the obtained graphene aerogel is 75.2%, and the content of cellulose nanocrystals is 24.8%;
note: the above% is by mass.
The density of the obtained graphene aerogel is 7.9mg/cm3The electromagnetic shielding effectiveness is 18dB, and the unit density electromagnetic shielding effectiveness is 2278dB cm3·g-1The energy loss coefficient from the compression curve after compression was 0.56.
Comparative example 5, the silver nanowires used in step 1 of example 6 were modified into carbon nanotubes, and the rest was identical to example 6.
The content of graphene in the obtained graphene aerogel is 76.4%, and the content of carbon nanotubes is 23.6%;
note: the above% is by mass.
The density of the obtained graphene aerogel is 7.67mg/cm3The electromagnetic shielding effectiveness is 25.9dB, and the unit density electromagnetic shielding effectiveness is 3377dB cm3·g-1The energy loss coefficient from the compression curve after compression was 0.50.
In conclusion, the preparation method solves the problems of high energy consumption and difficulty in uniform dispersion of the graphene and the composite aerogel thereof in the preparation process, greatly reduces the production cost, is expected to realize large-scale production of the graphene aerogel for electromagnetic shielding, and further widens the application field of the graphene aerogel for electromagnetic shielding by regulating and controlling the resilience.
Finally, it is also noted that the above-mentioned lists merely illustrate a few specific embodiments of the invention. It is obvious that the invention is not limited to the above embodiments, but that many variations are possible. All modifications which can be derived or suggested by a person skilled in the art from the disclosure of the present invention are to be considered within the scope of the invention.
Claims (2)
1. The preparation method of the elasticity-controllable graphene aerogel for electromagnetic shielding is characterized by sequentially carrying out the following steps of:
1) preparing raw materials:
graphene oxide aqueous dispersion: the concentration is 10mg/mL, and the size of the used graphene oxide is 5 μm;
silver nanowire aqueous dispersion: the concentration is 3mg/mL, the diameter of the silver nanowire is 60nm, and the length is 10 μm;
2) preparing a graphene oxide/silver nanowire aqueous dispersion:
slowly adding the silver nanowire aqueous dispersion into the graphene oxide aqueous dispersion under the stirring condition, continuously stirring for 10min to obtain uniformly and stably dispersed graphene oxide/silver nanowire aqueous dispersion, then adding a composite reducing agent, and stirring until ascorbic acid is dissolved to obtain a mixed solution;
the volume ratio of the graphene oxide aqueous dispersion to the silver nanowire aqueous dispersion is 1: 1;
the mass ratio of the composite reducing agent to the graphene oxide is 2:1, the composite reducing agent consists of ascorbic acid and tea polyphenol, wherein the ratio of ascorbic acid: the mass ratio of the tea polyphenol is 1: 1;
3) preparing the graphene aerogel:
3.1) placing the obtained mixed solution in a 60 ℃ oven to heat for 40min to obtain hydrogel I;
3.2) freezing the obtained hydrogel I at-20 ℃ for 2h, and then thawing at room temperature to obtain hydrogel II;
3.3) heating the obtained hydrogel II at 90 ℃ for 6h to obtain hydrogel III;
3.4) washing the obtained hydrogel III with water, removing unreacted ascorbic acid and other impurities, and then drying at 60 ℃ under normal pressure to obtain the graphene aerogel.
2. The elasticity-controllable graphene aerogel for electromagnetic shielding prepared by the method of claim 1.
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| 三维石墨烯_银纳米粒子气凝胶的构筑;李叶灿等;《青岛科技大学学报》;20180831;第39卷;第103-107页 * |
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