CN108003364B - Flexible graphene-based composite membrane, preparation method thereof and application of flexible graphene-based composite membrane as electromagnetic shielding material - Google Patents
Flexible graphene-based composite membrane, preparation method thereof and application of flexible graphene-based composite membrane as electromagnetic shielding material Download PDFInfo
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Abstract
The invention discloses a flexible graphene-based composite membrane, a preparation method thereof and application of the flexible graphene-based composite membrane as an electromagnetic shielding material, wherein the preparation method comprises the steps of treating graphene oxide and a solvent by a cell crusher, adding a silver/carbon nanofiber composite material and magnetic ferroferric oxide, treating by the cell crusher, adding a sodium alginate solution, and treating by the cell crusher to obtain a dispersion liquid; obtaining a composite film structure by the dispersion liquid through a vacuum filtration method; the thin film structure is placed in a closed kettle filled with a low-boiling-point liquid reducing agent, and is reduced by a fumigation method, so that the flexible graphene-based composite film with uniform component distribution, a porous structure and good flexibility is obtained, the electromagnetic shielding efficiency is good, the preparation method is simple and efficient in operation process, and the industrial production and application are easy to realize.
Description
Technical Field
The invention relates to an electromagnetic shielding material, in particular to a flexible graphene-based composite film and a preparation method and application thereof, and belongs to the field of preparation of electromagnetic shielding materials.
Background
Ferroferric oxide (Fe)3O4) As a main component of magnetite, there is a conventional magnetic material. Since ferroferric oxide has many excellent physicochemical properties as a non-metallic magnetic material which is the earliest application, ferroferric oxide is currently favored by researchers in the field of application and research of magnetic materials. At present, magnetic composite materials have been widely used in various fields, such as electromagnetic wave absorption, lithium ion batteries, targeted delivery of drugs, magnetic resonance imaging, high-efficiency circulating oil absorption materials and heavy metal ion adsorption. Ferroferric oxide functionalized composite materials are a great trend in the research field of magnetic materials.
Graphene materials have been receiving attention from material researchers because of their excellent properties such as a special two-dimensional structure, a large specific surface area, and a low density. The graphene with the two-dimensional layered structure has a large specific surface area, can be used as a base material, and is loaded with nanoparticles with special functions to functionalize the graphene. Relevant researches show that compared with the conventional spherical nano particles, the two-dimensional sheet structure of the graphene has more excellent wave-absorbing performance. Ferroferric oxide is used as a traditional wave absorbing material, and graphene and ferroferric oxide are prepared into Fe through a certain experimental method3O4The graphene composite material can integrate the advantages of the graphene composite material and the graphene composite material, and has wide application prospect in the field of wave-absorbing materials. At present, researchers of materials all over the world have prepared nano wave-absorbing materials by compounding graphene and magnetic ferroferric oxide, and have achieved certain achievements. For example, Chinese patent (CN106358429A) discloses a graphene-modified ferroferric oxide wave-absorbing material which comprises an impedance matching layer, a loss layer and a reflection layer from top to bottom, wherein the impedance matching layer is formed by graphene powder/ferroferric oxide powderThe impedance matching layer is formed by dispersing hydroxyl iron powder into chloroprene rubber, the reflecting layer is formed by dispersing graphite into chloroprene rubber, and the impedance matching layer contains 2-5% of graphene powder/ferroferric oxide powder. When the thickness of the wave-absorbing material is 0.2mm, the maximum absorption of the wave-absorbing material exceeds-9.46 dB, and the wave-absorbing material has excellent performance. Chinese patent (CN106118594A) discloses a preparation method of a graphene oxide/ferroferric oxide composite material, wherein the graphene oxide/ferroferric oxide composite material is obtained by specific heating and ultrasonic steps under the condition of only adopting heating and ultrasonic waves without any reducing agent; the ferroferric oxide nano particles prepared by the method are closely arranged and uniformly dispersed to form a structure similar to the surface of a steel file, the problem of dispersion among graphene sheet layers is effectively solved, and uniform dispersion of the ferroferric oxide nano particles on the surface of graphene and uniform dispersion among the graphene sheet layers are realized. The adsorption is better in the frequency range of 2-18 GHz, for example, the adsorption is maximum at 10.28GHz, the maximum absorption is-34.95 dB, the wave absorption is less than-10 dB in the frequency range of 5.72-7.88 GHz, and the effective absorption width is 2.1 GHz. The graphene/ferroferric oxide composite material prepared by the method is mainly of a compact structure, is of an inflexible structure and is poor in conductivity.
Disclosure of Invention
Aiming at the defects of ferroferric oxide/graphene composite materials as wave absorbing materials in the prior art, the invention aims to provide a flexible graphene-based composite film which is light, flexible, wide in applicable frequency band and good in electromagnetic shielding effect, and the flexible graphene-based composite film meets the application requirements of the electromagnetic shielding materials on thinness, lightness, width and strength.
Another object of the present invention is to provide a method for preparing the flexible graphene-based composite membrane, which is simple to operate and low in cost.
The third purpose of the present invention is to provide an application of the flexible graphene-based composite film as an electromagnetic shielding material, wherein the flexible graphene-based composite film has characteristics of light weight, flexibility, wide applicable frequency band, good electromagnetic shielding effect, and the like, and meets application requirements of the electromagnetic shielding material on thinness, lightness, width, and strength.
In order to achieve the technical purpose, the invention provides a preparation method of a flexible graphene-based composite film, which comprises the following steps:
1) mixing graphene oxide with a solvent, and treating the mixture by using a cell crusher to obtain a dispersion liquid A;
2) adding a silver/carbon nanofiber composite material and magnetic ferroferric oxide into the dispersion liquid A, and treating by using a cell crusher to obtain a dispersion liquid B;
3) adding the sodium alginate solution into the dispersion liquid B, and treating by using a cell crusher to obtain a dispersion liquid C;
4) carrying out vacuum filtration on the dispersion liquid C to obtain a composite film structure;
5) and (3) placing the composite film structure in a closed kettle filled with a low-boiling-point liquid reducing agent, and reducing by a fumigation method to obtain the composite film.
In a preferable scheme, the treatment time of the cell crusher in the step 1) is 10-30 min.
In a preferable scheme, the treatment time of the cell crusher in the step 2) is 10-30 min.
In a preferable scheme, the treatment time of the cell crusher in the step 3) is 10-30 min.
In the preferred scheme, the addition amount of the silver/carbon nanofiber composite material is 18-43% of the total mass of the graphene oxide, the silver/carbon nanofiber composite material and the magnetic ferroferric oxide.
In the preferred scheme, the addition amount of the magnetic ferroferric oxide is 12-30% of the total mass of the graphene oxide, the silver/carbon nanofiber composite and the magnetic ferroferric oxide.
In a more preferable scheme, the magnetic ferroferric oxide is obtained by a chemical coprecipitation method.
In a more preferable scheme, the silver/carbon nanofiber composite material is obtained by a chemical deposition method.
In a preferred embodiment, the graphene oxide is obtained by a Hummer method.
In a preferable scheme, the concentration of the sodium alginate solution is 0.5-1.25 mg/mL; the mass of the sodium alginate is 0.5-1.5 times of that of the graphene oxide.
In a preferred embodiment, the low-boiling point liquid reducing agent is hydrazine hydrate.
In a preferred embodiment, the conditions of the fumigation reduction are as follows: the temperature is 90-120 ℃, and the time is 8-10 h.
The invention also provides a flexible graphene-based composite membrane prepared by the method.
According to the preferred scheme, the flexible graphene-based composite membrane has a porous structure, and graphene, the silver/carbon nanofiber composite material and the magnetic ferroferric oxide in the flexible graphene-based composite membrane are uniformly distributed.
The invention also provides application of the flexible graphene-based composite film as an electromagnetic shielding material.
The preparation method of the flexible graphene-based composite membrane comprises the following specific steps:
(1) weighing 30-52 wt% of graphene oxide (measured by taking the total mass of the graphene oxide, the silver/carbon nanofiber composite and the magnetic ferroferric oxide as 100%) according to the mass fraction, adding the graphene oxide into a beaker, adding a proper amount of absolute ethyl alcohol, and working for 10-30 min under a cell crusher to obtain a uniform dispersion liquid; respectively adding 18-46 wt% of silver-loaded carbon nano fiber and 10-35 wt% of magnetic ferroferric oxide powder according to mass fraction, and continuously dispersing the mixed solution by using a cell crusher;
(2) uniformly dispersing sodium alginate powder into distilled water to obtain a sodium alginate solution with the concentration of 0.5-1.25 mg/mL (the mass of the sodium alginate is 0.5-1.5 times of that of the graphene oxide), mixing the sodium alginate solution with the dispersion liquid obtained in the step (1), and then operating for 10-30 min under a cell crusher;
(3) filtering the mixed solution obtained in the step (2) by adopting a vacuum filtration method, filtering by adopting an organic microporous filter membrane with the size of 50mm x 0.22 mu m to obtain a composite film, and standing and drying for 8-12 h at normal temperature and normal pressure;
(4) and (4) removing the film obtained in the step (3), sealing and placing the film into a polytetrafluoroethylene-lined stainless steel autoclave dropwise added with a proper amount of hydrazine hydrate, heating to 90-120 ℃, carrying out reduction reaction for 8-10 hours, cooling to room temperature, and taking out to obtain the flexible graphene-based composite film.
According to the technical scheme, the flexible graphene-based composite membrane takes graphene as a matrix, the magnetic ferroferric oxide particles and the silver/carbon nanofiber composite material as doping materials, and the materials are bonded and molded by sodium alginate, so that a membrane material which is good in flexibility, uniform in component distribution and porous in structure is obtained, and the membrane material has good electromagnetic shielding effect through testing and is suitable for production and application. Compared with the existing graphene/ferroferric oxide composite material, the flexible graphene-based composite film has the greatest characteristics of better flexibility and doping of silver-loaded carbon nanofibers, and the silver-loaded carbon nanofibers have high conductivity and do not have wave-absorbing property when being used alone, but are filled between ferroferric oxide with magnetic loss and graphene with dielectric loss to generate dielectric polarization, and the three components have complementary advantages to obtain the efficient electromagnetic shielding material. In addition, sodium alginate is used as a binder, which is present in large amounts in the form of-COO-with-OH-The group can form a coordination compound with polyvalent metal ions, so that when the content of the metal ions in the sodium alginate matrix is increased to a certain degree, the binding force between the ions is enhanced, the electrostatic repulsion effect between the ions is overcome enough, the ions are mutually connected to form a conductive particle chain, the electromagnetic shielding and antistatic capabilities of the fabric are improved, and the sodium alginate is used as a binder of the graphene, magnetic ferroferric oxide particles and silver/carbon nanofiber composite materials to obtain the electromagnetic shielding flexible fabric.
The flexible graphene-based composite film has a porous structure, and has a good electromagnetic shielding effect compared with a compact graphene-based composite film prepared by other methods, mainly because the microwave obtained from the porous structure is absorbed through multiple scattering and reflection. Hydrazine hydrate vapor is reduced to have a microporous structure, so that electromagnetic waves are absorbed more rather than reflected back from the foam, and the hydrazine hydrate vapor is a better wave absorber. The electromagnetic shielding effect is nearly 24dB at the low thickness of 120 μm, and at least 99% of electromagnetic wave radiation can be blocked.
Compared with the prior art, the invention has the technical effects that:
(a) according to the invention, a hydrazine hydrate steam reduction mode is adopted to reduce graphene oxide into reduced graphene oxide, and silver-loaded carbon nanofibers are added, so that the conductivity of the carbon nanofibers is increased from 1.7-2.1S/m to 52-56S/m, and the improvement of a proper amount of conductivity is beneficial to the enhancement of the electromagnetic shielding effect.
(b) According to the invention, a hydrazine hydrate steam reduction mode is adopted, the composite membrane is propped open and is changed into a porous state from a compact state, and the porous structure can enhance microwave absorption through multiple scattering and reflection, so that the electromagnetic shielding device has higher electromagnetic shielding efficiency.
(c) According to the invention, sodium alginate is used as the binder, so that the electromagnetic shielding effect is improved, and the flexibility and the formability of the composite film are effectively improved.
(d) The graphene powder material prepared by the invention has the advantages of strong wave absorption capability, wide wave absorption frequency band, small density, small thickness and stable performance. Some embodiments show that the wave-absorbing material has a total electromagnetic shielding effectiveness of over 20dB in an X wave band, and can block 99% of electromagnetic wave radiation. The finished product has good uniformity, controllable size, simple process and low cost, and meets the requirements of industrial production.
Drawings
Fig. 1 is a schematic view showing a comparison of microscopic cross sections of the composite film of example 1 before and after reduction.
Fig. 2 is a schematic view showing a comparison of microscopic cross sections of the composite film of example 2 of the present invention before and after reduction.
Fig. 3 is a schematic view showing a comparison of microscopic cross sections of the composite film of example 3 of the present invention before and after reduction.
Fig. 4 is an electromagnetic shielding performance diagram of application example 1 of the present invention.
Fig. 5 is an electromagnetic shielding performance diagram of application example 2 of the present invention.
Fig. 6 is a schematic view showing a microscopic surface of the graphene-based composite film according to the present invention.
Fig. 7 is a schematic diagram showing the comparison of the electrical conductivity before and after the reduction of the graphene-based composite film according to the present invention.
Fig. 8 is a schematic view of a macroscopic morphology of the graphene-based composite film according to the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments, and all other embodiments obtained by those skilled in the art without any creative work based on the embodiments of the present invention belong to the protection scope of the present invention.
The following are some examples of the inventors in their experiments:
example 1
(1) Weighing 30mg of graphene oxide, adding the graphene oxide into a beaker, adding 160ml of absolute ethyl alcohol, and working for 15min under a cell crusher to obtain a uniform dispersion liquid. And then adding 33 wt% of silver-loaded carbon nano fiber and 17 wt% of magnetic ferroferric oxide powder according to mass fraction, and continuously dispersing the mixed solution by using a cell crusher.
(2) And (3) uniformly dispersing 30mg of sodium alginate powder into 40ml of distilled water, mixing with the dispersion liquid obtained in the step (1), and working for 15min under a cell crusher.
(3) And (3) carrying out vacuum filtration on the mixed solution obtained in the step (2) to obtain a composite film, and standing and drying for 12 hours at normal temperature and normal pressure.
(4) And (4) removing the film obtained in the step (3), sealing and placing the film into a polytetrafluoroethylene lining stainless steel autoclave dropwise added with 4 drops of hydrazine hydrate, heating to 100 ℃, keeping the constant temperature for 9 hours, cooling to room temperature, and taking out to obtain the flexible graphene-based composite film.
FIG. 1 is a schematic diagram showing the comparison of microscopic cross sections before and after reduction of a composite membrane, wherein the cross section is changed from a compact structure to a porous structure, and the thickness is increased from 66.52-70.50 μm to 110.67-129.33 μm. Due to the reduction effect of hydrazine hydrate, the graphene basal lamina is spread.
Example 2
(1) Weighing 30mg of graphene oxide, adding the graphene oxide into a beaker, adding 160ml of absolute ethyl alcohol, and working for 15min under a cell crusher to obtain a uniform dispersion liquid. And then 43 wt% of silver-loaded carbon nanofiber and 14 wt% of magnetic ferroferric oxide powder are added according to mass fraction, and the mixed solution is continuously dispersed by using a cell crusher.
(2) And (3) uniformly dispersing 30mg of sodium alginate powder into 40ml of distilled water, mixing with the dispersion liquid obtained in the step (1), and working for 15min under a cell crusher.
(3) And (3) carrying out vacuum filtration on the mixed solution obtained in the step (2) to obtain a composite film, and standing and drying for 12 hours at normal temperature and normal pressure.
(4) And (4) removing the film obtained in the step (3), sealing and placing the film into a polytetrafluoroethylene lining stainless steel autoclave dropwise added with 4 drops of hydrazine hydrate, heating to 110 ℃, keeping the constant temperature for 9 hours, cooling to room temperature, and taking out to obtain the flexible graphene-based composite film.
FIG. 2 is a schematic diagram showing the comparison of microscopic cross sections before and after reduction of the composite membrane, wherein the cross section is changed from a compact structure to a porous structure, and the thickness is increased from 70.67-86.67 μm to 112.00-135.20 μm. Due to the reduction effect of hydrazine hydrate, the graphene basal lamina is spread.
Example 3
(1) Weighing 30mg of graphene oxide, adding the graphene oxide into a beaker, adding 160ml of absolute ethyl alcohol, and working for 15min under a cell crusher to obtain a uniform dispersion liquid. And then adding 33 wt% of silver-loaded carbon nanofiber and 33 wt% of magnetic ferroferric oxide powder according to mass fraction, and continuously dispersing the mixed solution by using a cell crusher.
(2) And (3) uniformly dispersing 30mg of sodium alginate powder into 40ml of distilled water, mixing with the dispersion liquid obtained in the step (1), and working for 15min under a cell crusher.
(3) And (3) carrying out vacuum filtration on the mixed solution obtained in the step (2) to obtain a composite film, and standing and drying for 12 hours at normal temperature and normal pressure.
(4) And (4) removing the film obtained in the step (3), sealing and placing the film into a polytetrafluoroethylene-lined stainless steel autoclave dropwise added with 4 drops of hydrazine hydrate, heating to 120 ℃, keeping the constant temperature for 9 hours, cooling to room temperature, and taking out to obtain the flexible graphene-based composite film.
FIG. 3 is a schematic diagram showing the comparison of microscopic cross sections before and after reduction of the composite membrane, wherein the cross section is changed from a compact structure to a porous structure, and the thickness is increased from 72.67-98.01 μm to 119.20-124.00 μm. Due to the reduction effect of hydrazine hydrate, the graphene basal lamina is spread.
Application example 1
In order to measure the electromagnetic shielding performance, the S parameter (S) of the sample, was investigated in the X band by using a rectangular waveguide method at room temperature11And S21) Measured by a vector network analyzer (N5230C). The flexible graphene-based composite film obtained in example 2 was cut to an appropriate size (corresponding to the size of an X-band waveguide sheet, 22.86 × 10.16mm), adhered to a paraffin substrate, and placed on a support. (since the paraffin block is a wave-transparent material and only acts as a matrix in the measurement, the measured electromagnetic parameters can be considered to be entirely due to the thin film).
Determining SE from measured S parametersTAnd SEAAnd SERThe following were used:
R＝|S11|2，T＝|S21|2.
A＝1-R-T
SER(dB)＝-10log(1-R)
SEA(dB)＝-10log(T/(1-R))
SET(dB)＝SER+SEA
where R is the reflection coefficient, T is the transmission coefficient, and A is the absorption coefficient.
The resulting electromagnetic shielding effectiveness is shown in fig. 4, with a total electromagnetic shielding effectiveness of approximately 20 dB.
Application example 2
In order to measure the electromagnetic shielding performance, the S parameter (S) of the sample, was investigated in the X band by using a rectangular waveguide method at room temperature11And S21) Measured by a vector network analyzer (N5230C). The flexible graphene-based composite film obtained in example 3 was cut to an appropriate size (corresponding to the size of an X-band waveguide sheet, 22.86 × 10.16mm), adhered to a paraffin substrate, and placed on a support. (since the paraffin block is a wave-transparent material and only acts as a matrix in the measurement, the measured electromagnetic parameters can be considered to be entirely due to the thin film).
Determining SE from measured S parametersTAnd SEAAnd SERThe following were used:
R＝|S11|2，T＝|S21|2.
A＝1-R-T
SER(dB)＝-10log(1-R)
SEA(dB)＝-10log(T/(1-R))
SET(dB)＝SER+SEA
wherein R is the reflection coefficient, T is the transmission coefficient, A is the absorption coefficient
The final electromagnetic shielding effectiveness is shown in fig. 5, the total electromagnetic shielding effectiveness is close to 24dB, the performance is better, and the total electromagnetic shielding effectiveness is mainly due to the increase of the mass fraction of ferroferric oxide compared with the application example 1.
Claims (7)
1. A preparation method of a flexible graphene-based composite film is characterized by comprising the following steps: the method comprises the following steps:
1) mixing graphene oxide with a solvent, and treating the mixture by using a cell crusher to obtain a dispersion liquid A;
2) adding a silver/carbon nanofiber composite material and magnetic ferroferric oxide into the dispersion liquid A, and treating by using a cell crusher to obtain a dispersion liquid B; the addition amount of the silver/carbon nanofiber composite material is 18-43% of the total mass of the graphene oxide, the silver/carbon nanofiber composite material and the magnetic ferroferric oxide, and the addition amount of the magnetic ferroferric oxide is 12-30% of the total mass of the graphene oxide, the silver/carbon nanofiber composite material and the magnetic ferroferric oxide;
3) adding the sodium alginate solution into the dispersion liquid B, and treating by using a cell crusher to obtain a dispersion liquid C;
4) carrying out vacuum filtration on the dispersion liquid C to obtain a composite film structure;
5) placing the composite film structure in a closed kettle filled with a low-boiling-point liquid reducing agent, and reducing by a fumigation method to obtain the composite film structure; the low-boiling-point liquid reducing agent is hydrazine hydrate; the conditions of the fumigation reduction are as follows: the temperature is 90-120 ℃, and the time is 8-10 h.
2. The method for preparing a flexible graphene-based composite film according to claim 1, wherein:
the treatment time of the cell crusher in the step 1) is 10-30 min;
the time for the cell crusher in the step 2) to process is 10-30 min;
the time for the cell crusher in the step 3) to process is 10-30 min.
3. The method for preparing a flexible graphene-based composite film according to claim 1, wherein: the magnetic ferroferric oxide is obtained by a chemical coprecipitation method;
the silver/carbon nanofiber composite material is obtained by a chemical deposition method.
4. The method for preparing a flexible graphene-based composite film according to claim 1, wherein: the concentration of the sodium alginate solution is 0.5-1.25 mg/mL; the mass of the sodium alginate is 0.5-1.5 times of that of the graphene oxide.
5. A flexible graphene-based composite film is characterized in that: prepared by the method of any one of claims 1 to 4.
6. The flexible graphene-based composite film according to claim 5, wherein: the flexible graphene-based composite membrane has a porous structure, and the components of graphene, the silver/carbon nanofiber composite material and the magnetic ferroferric oxide in the flexible graphene-based composite membrane are uniformly distributed.
7. Use of a flexible graphene-based composite film according to claim 5 or 6, wherein: the material is applied as an electromagnetic shielding material.
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