CN110407196B - Preparation method of low-defect graphene film based on graphene foam - Google Patents
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Abstract
The invention discloses a preparation method of a low-defect graphene film based on graphene foam, which comprises the following steps: step one, preparing anisotropic graphene oxide frozen foam; step two, preparing anisotropic graphene oxide foam; step three, reducing the graphene oxide film; step four, preparing a graphene carbon film; and step five, preparing the low-defect graphene film based on the graphene foam. The method has the advantages of simple process and low cost, the graphene oxide is used as a raw material, the area of the lamella is large and adjustable, and the continuous lamella structure reduces the crystal boundary scattering of phonons in the transmission process, thereby being beneficial to improving the thermal conductivity. The method can prepare the graphene film with low defect based on the graphene foam, which has the advantages of uniform graphene dispersion, certain flexibility, high heat conduction and high mechanical strength, and is suitable for the development requirements of the current scientific technology.
Description
Technical Field
The invention belongs to the technical field of material science, and relates to a preparation method of a low-defect graphene film based on graphene foam.
Background
Graphene is another stable nano carbon simple substance after fullerene and carbon nano tube, is an ideal two-dimensional planar material, and has excellent electrical, mechanical and thermal properties. The transmission of free electrons on the graphene is not easy to scatter, and the electron mobility can reach 2 multiplied by 105cm/v.s, which is more than one hundred times the electron mobility in silicon; the conductivity of the material is up to 106S/m, is an excellent conductive material at room temperature. The elastic modulus of the graphene is up to 1 TPa, the breaking strength is 125 GPa, and the room-temperature thermal conductivity is 5.3 multiplied by 103W/m.K, specific surface area 2630 m2(ii) in terms of/g. Graphene also has excellent optical properties, and the visible light absorption rate of single-layer graphene is only 2.3%, so that the number of layers of graphene can be estimated according to the visible light transmission rate of thin-layer graphene. In addition, the ultraviolet light has an etching effect on the graphene, and the ultraviolet light irradiates for a long timeThe graphene film is increasingly damaged, and the visible light transmittance and the film sheet resistance of the graphene film are increased. The two-dimensional graphene film has high conductivity and transmittance, and also has excellent chemical stability and thermal stability, and can be used as a substitute for a solar transparent electrode. Therefore, the graphene has a great application value in the fields of composite materials, catalytic materials, energy storage materials, high-function nano-electronic devices, gas sensors and the like, and also attracts numerous scholars to carry out deep and systematic research on the graphene.
The graphene film is one of macroscopical bodies for realizing application of graphene, and raw materials used for assembling the graphene film at present comprise graphene and graphene oxide. The graphene has good crystallinity, the few-layer graphene prepared by mechanical stripping or a CVD method has less defect content and excellent heat conduction and electric conduction performance, but the graphene has larger specific surface area and is easy to agglomerate, and the uniformity and various performances of the graphene film are greatly influenced. Therefore, when graphene is used to prepare a graphene film, the graphene is often modified or an organic dispersant is added to improve the dispersibility of the graphene. Due to the lack of effective interaction between the graphene nano sheets, the graphene nano sheets can be combined only through weak van der Waals force between the sheets, and the mechanical property of the assembled graphene film is greatly reduced. Another assembling method of the graphene film is to assemble the graphene oxide film by using graphene oxide, and then reduce the graphene oxide film to obtain the graphene film. The graphene oxide contains rich oxygen-containing functional groups, can be uniformly dispersed in an organic solvent and an aqueous solution, and improves the dispersibility of the graphene. The graphene oxide film has the advantages that the graphene oxide sheet layer has large and adjustable area, the continuous sheet structure reduces the crystal boundary scattering of phonons in the transmission process, the improvement of the thermal conductivity is facilitated, and in addition, the rich oxygen-containing functional groups on the graphene oxide sheet layer can interact to generate strong interactions such as hydrogen bonds, conjugated large pi bonds and the like to improve the mechanical property of the graphene film.
The conventional methods for preparing graphene film materials mainly comprise a chemical vapor deposition method (CVD), a vacuum filtration method, a self-assembly method, a spin-coating method, an epitaxial growth method, a spraying method, a micro-mechanical stripping method, a liquid phase stripping method and the like, wherein the chemical vapor deposition method is adopted at the earliest time, the method essentially belongs to the gaseous mass transfer process of the atomic category, and the film prepared by the method has good crystallinity, less impurities, but is limited by a substrate, the thickness cannot be increased, and no interaction exists among sheet layers, so that the mechanical property is poor. Vacuum filtration is also one of the commonly used methods, and generally a microporous mixed fiber membrane or an alumina filter membrane is used for filtration. The film has high quality and thin thickness, but the method takes long time and cannot prepare a large-area film due to the limitation of suction filtration equipment. In view of the present, spin coating is a common and efficient method for preparing thin films, and is generally disposed on a planar substrate, and under the action of shearing force, the prepared thin films are very uniform and have high orientation, but the thin films are difficult to separate from the substrate, and the thickness is greatly influenced by the solution concentration and the speed of a spin coater. The evaporation self-assembly method can prepare a film in a large size, and researches show that when the graphene oxide dispersion liquid is subjected to evaporation at a high temperature, a lamellar layer can form a film at a gas-liquid interface, but the drying is slow, the period required by experiments is long, and the size of the lamellar layer of the film is uneven and the mechanical strength is poor due to the influence of the Tyndall effect in the evaporation process. Epitaxial growth provides high quality multilayer graphene samples that interact strongly with their substrates, however, these assembled graphene films exhibit relatively poor performance due to poor interlayer junction contact resistance and structural defects formed during severe exfoliation and reduction.
In conclusion, the existing preparation method of the graphene film lacks a method which is simple to operate, low in cost, capable of solving the problem of graphene dispersion, and capable of improving mechanical strength and simultaneously considering high thermal conductivity and flexibility.
Disclosure of Invention
In order to solve the problems of mechanical property and electric and heat conducting property of the existing graphene film, the invention provides a preparation method of a low-defect graphene film based on graphene foam. The method can be used for preparing the graphene film with low defects based on the graphene foam, wherein the graphene film is uniformly dispersed, has certain flexibility, high heat conductivity and high mechanical strength, and meets the development requirements of the current scientific technology.
The purpose of the invention is realized by the following technical scheme:
a preparation method of a low-defect graphene film based on graphene foam comprises the following steps:
step one, preparing a graphene oxide aqueous solution:
taking graphene oxide slurry as a raw material, adding deionized water, stirring for 60-120 min at a stirring speed of 100-700 r/min, and then carrying out ultrasonic treatment for 30-60 min at a frequency of 10-100 KHz to obtain a graphene oxide aqueous solution, wherein: the concentration of the graphene oxide slurry is 20 mg/mL; in the graphene oxide aqueous solution, the concentration of the graphene oxide is 1-10 mg/mL, preferably 3-7 mg/mL;
step two, preparing anisotropic graphene oxide frozen foam:
directionally freezing the graphene oxide aqueous solution by using liquid nitrogen to obtain anisotropic graphene oxide freezing foams with different shapes, wherein: the directional freezing is an ice separation induced self-assembly method;
step three, preparing anisotropic graphene oxide foam:
by using CO2Drying the anisotropic graphene oxide frozen foam by a supercritical drying method to obtain the anisotropic graphene oxide foam, wherein: the drying mode is a freeze drying method;
step four, reducing the graphene oxide film:
placing anisotropic graphene oxide foam in a hot-pressing reaction furnace, and reducing graphene oxide by adopting a hot-pressing oxidation pretreatment process, namely: when the temperature is raised to 250 ℃, mechanical pressurization is carried out, and the pressure is controlled to be 20-30 MPa; and continuously heating to 350-400 ℃, keeping the temperature for 1-1.5 h, then cooling, when the temperature is as low as 250 ℃, removing the pressure, and continuously cooling to the room temperature to obtain the reduced graphene oxide film, wherein: the preparation method of the reduced graphene oxide film is called a dimensionality reduction method;
step five, preparing the graphene carbon film:
placing the reduced graphene oxide film in a hot-pressing reaction furnace, and realizing the carbonization of graphene by adopting a high-temperature vacuum heat treatment process, namely: when the temperature is raised to 250 ℃, mechanical pressurization is carried out, and the pressure is controlled to be 20-30 MPa; continuously heating to 800-1000 ℃, keeping the temperature for 2-2.5 h, then cooling, when the temperature is as low as 250 ℃, removing the pressure, and continuously cooling to room temperature to obtain the graphene carbon film;
step six, preparing a low-defect graphene film based on graphene foam:
placing a graphene carbon film in a high-temperature graphitization furnace, and adopting a gradient heating method to realize graphitization of the carbon film, namely: heating to 1000-1200 ℃ at a heating rate of 20 ℃/min, heating to 2000-2200 ℃ at a heating rate of 10 ℃/min instead, keeping the temperature for 30-35 min, heating to 2800-3000 ℃ at a heating rate of 5 ℃/min, keeping the temperature for 115-120 min, and cooling to room temperature to obtain the low-defect graphene film based on the graphene foam.
Compared with the prior art, the invention has the following advantages:
1. the method has the advantages that the process is simple, the cost is low, the graphene oxide is used as a raw material, the area of the sheet layer is large and adjustable, the continuous sheet layer structure reduces the crystal boundary scattering of phonons in the transmission process, and the heat conductivity is improved;
2. according to the invention, the three-dimensional graphene oxide foam with directional arrangement is prepared by adopting an ice separation induction self-assembly method and a freeze drying technology, so that the problem of the dispersibility of graphene is improved;
3. the method adopts a dimensionality reduction method, and obtains the graphene film with low defects based on the graphene foam through a hot-pressing oxidation pretreatment process, a high-temperature vacuum heat treatment process and a graphitization treatment process, so that effective interface contact is established, stronger interaction is generated among sheet layers, the mechanical property of the film is improved, the thermal conductivity and the electric conductivity of the film are improved, and the thermal conductivity and the electric conductivity are more stable and excellent;
4. the graphene foam-based low-defect graphene film prepared by the invention can control the thickness and flexibility of the graphene film by adjusting the concentration of the dispersion liquid, mechanical pressure, heat treatment temperature and reaction time.
Drawings
Fig. 1 is a photograph of an anisotropic graphene oxide foam prepared in example 1;
fig. 2 is a photograph of a graphene foam-based low-defect graphene thin film prepared in example 1 and its flexibility;
fig. 3 is a schematic flow chart of the preparation process of the graphene foam-based low-defect graphene thin film obtained in example 1.
Detailed Description
The technical solutions of the present invention are further described below with reference to the following examples, but the present invention is not limited thereto, and any modifications or equivalent substitutions may be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.
Example 1:
in this embodiment, as shown in fig. 3, the preparation method of the low-defect graphene film based on the graphene foam is specifically performed according to the following steps:
step one, preparing a graphene oxide aqueous solution:
measuring 20mL of graphene oxide slurry with the concentration of 20mg/mL, and adding deionized water; stirring for 60min under the condition that the stirring speed is 700 r/min; and then, carrying out ultrasonic treatment for 30min under the condition that the frequency is 100KHz to obtain a graphene oxide aqueous solution with the graphene oxide concentration of 5 mg/mL.
Step two, preparing anisotropic graphene oxide frozen foam:
and (3) directionally freezing the graphene oxide aqueous solution by using liquid nitrogen to obtain anisotropic graphene oxide freezing foams with different shapes.
Step three, preparing anisotropic graphene oxide foam:
by using CO2And drying the anisotropic graphene oxide frozen foam by a supercritical drying method to obtain the anisotropic graphene oxide foam.
Step four, reducing the graphene oxide film:
placing the anisotropic graphene oxide composite foam in a hot-pressing reaction furnace, and reducing graphene oxide by adopting a hot-pressing oxidation pretreatment process; when the temperature is raised to 250 ℃, mechanical pressurization is carried out, and the pressure is 25 MPa; continuously heating to 400 ℃, keeping the temperature for 1h, then cooling, and when the temperature is as low as 250 ℃, removing the pressure; and continuously cooling to room temperature to obtain the reduced graphene oxide film.
Step five, preparing the graphene carbon film:
placing the reduced graphene oxide film in a hot-pressing reaction furnace, and carbonizing graphene by adopting a high-temperature vacuum heat treatment process; when the temperature is raised to 250 ℃, mechanical pressurization is carried out, and the pressure is 25 MPa; continuously heating to 1000 ℃, keeping the temperature for 2 hours, then cooling, and when the temperature is lowered to 250 ℃, removing the pressure; and continuously cooling to room temperature to obtain the graphene carbon film.
Step six, preparing a low-defect graphene film based on graphene foam:
placing the graphene carbon film in a high-temperature graphitization furnace, and adopting a gradient heating method to realize graphitization of the carbon film; heating to 1200 ℃ at a heating rate of 20 ℃/min, heating to 2200 ℃ at a heating rate of 10 ℃/min instead, keeping the temperature for 30min, heating to 2800 ℃ continuously at a heating rate of 5 ℃/min, keeping the temperature for 120min, and cooling to room temperature to obtain the low-defect graphene film based on the graphene foam.
The photo of the anisotropic graphene oxide foam prepared in the third step of this embodiment is shown in fig. 1, and it can be seen from the photo that the anisotropic graphene oxide foam is black and gray, and has a flat surface, the cut graphene oxide sheet layer inside is in an oriented tube bundle structure along the growth direction of the ice crystals, and the vertical direction is in a cellular-like hole structure, which has a positive effect on the formation of the low-defect graphene film based on the graphene foam at the later stage.
The photo of the graphene foam-based low-defect graphene film prepared in the sixth step of the present embodiment and the flexible photo thereof are shown in fig. 2, and it can be seen from the photo that the prepared graphene foam-based low-defect graphene film has a smooth surface, is metallic luster, and has a certain flexibility, and can be bent by 180 ° and folded into various shapes.
In the embodiment, the thermal conductivity and the electric conductivity of the sample are tested to obtain the thermal conductivity of the low-defect graphene film based on the graphene foam to be 1150W m-1 K-1The conductivity reaches 1.25 multiplied by 105 S m-1Meanwhile, the graphene foam-based low-defect graphene film prepared by the embodiment has higher tensile strength, reaches 76MPa, is lower in raw material cost compared with the existing graphene film which can exist independently, is uniform in dispersion of the prepared graphene, has higher heat conduction performance, electric conduction performance and excellent mechanical strength, has certain flexibility, and meets the actual application requirements in the fields of national defense and military equipment and intelligent electronics.
Example 2:
in this embodiment, the preparation method of the low-defect graphene film based on the graphene foam is specifically performed according to the following steps:
step one, preparing a graphene oxide aqueous solution:
measuring 20mL of graphene oxide slurry with the concentration of 20mg/mL, and adding deionized water; stirring for 60min under the condition that the stirring speed is 700 r/min; and then, carrying out ultrasonic treatment for 30min under the condition that the frequency is 100KHz to obtain a graphene oxide aqueous solution with the graphene oxide concentration of 5 mg/mL.
Step two, preparing anisotropic graphene oxide frozen foam:
and (3) directionally freezing the graphene oxide aqueous solution by using liquid nitrogen to obtain anisotropic graphene oxide freezing foams with different shapes.
Step three, preparing anisotropic graphene oxide foam:
by using CO2And drying the anisotropic graphene oxide frozen foam by a supercritical drying method to obtain the anisotropic graphene oxide foam.
Step four, reducing the graphene oxide film:
placing the anisotropic graphene oxide composite foam in a hot-pressing reaction furnace, and reducing graphene oxide by adopting a hot-pressing oxidation pretreatment process; when the temperature is raised to 250 ℃, mechanical pressurization is carried out, and the pressure is 30 MPa; continuously heating to 400 ℃, keeping the temperature for 1h, then cooling, and when the temperature is as low as 250 ℃, removing the pressure; and continuously cooling to room temperature to obtain the reduced graphene oxide film.
Step five, preparing the graphene carbon film:
placing the reduced graphene oxide film in a hot-pressing reaction furnace, and carbonizing graphene by adopting a high-temperature vacuum heat treatment process; when the temperature is raised to 250 ℃, mechanical pressurization is carried out, and the pressure is 30 MPa; continuously heating to 1000 ℃, keeping the temperature for 2 hours, then cooling, and when the temperature is lowered to 250 ℃, removing the pressure; and continuously cooling to room temperature to obtain the graphene carbon film.
Step six, preparing a low-defect graphene film based on graphene foam:
placing the graphene carbon film in a high-temperature graphitization furnace, and adopting a gradient heating method to realize graphitization of the carbon film; heating to 1000 ℃ at a heating rate of 20 ℃/min, heating to 2000 ℃ at a heating rate of 10 ℃/min instead, keeping the temperature for 35min, heating to 3000 ℃ continuously at a heating rate of 5 ℃/min, keeping the temperature for 115min, and cooling to room temperature to obtain the low-defect graphene film based on the graphene foam.
In the embodiment, the thermal conductivity and the electric conductivity of the sample are tested to obtain the thermal conductivity of the low-defect graphene thin film based on the graphene foam being 1050W m-1 K-1The conductivity reaches 1.2 multiplied by 105 S m-1Simultaneously, the low-defect graphene film based on the graphene foam prepared by the embodiment has higher tensile strength, reaches 70MPa, is compared with the existing graphene film which can exist independently, has low raw material cost, is uniformly dispersed in the prepared graphene, simultaneously has higher heat conduction and electric conduction performance and excellent mechanical strength, has certain flexibility, and meets the actual application requirements in the fields of national defense and military equipment and intelligent electronics.
Example 3:
in this embodiment, the preparation method of the low-defect graphene film based on the graphene foam is specifically performed according to the following steps:
step one, preparing a graphene oxide aqueous solution:
measuring 20mL of graphene oxide slurry with the concentration of 20mg/mL, and adding deionized water; stirring for 60min under the condition that the stirring speed is 700 r/min; and then, carrying out ultrasonic treatment for 30min under the condition that the frequency is 100KHz to obtain a graphene oxide aqueous solution with the graphene oxide concentration of 5 mg/mL.
Step two, preparing anisotropic graphene oxide frozen foam:
and (3) directionally freezing the graphene oxide aqueous solution by using liquid nitrogen to obtain anisotropic graphene oxide freezing foams with different shapes.
Step three, preparing anisotropic graphene oxide foam:
by using CO2And drying the anisotropic graphene oxide frozen foam by a supercritical drying method to obtain the anisotropic graphene oxide foam.
Step four, reducing the graphene oxide film:
placing the anisotropic graphene oxide composite foam in a hot-pressing reaction furnace, and reducing graphene oxide by adopting a hot-pressing oxidation pretreatment process; when the temperature is raised to 250 ℃, mechanical pressurization is carried out, and the pressure is 20 MPa; continuously heating to 400 ℃, keeping the temperature for 1h, then cooling, and when the temperature is as low as 250 ℃, removing the pressure; and continuously cooling to room temperature to obtain the reduced graphene oxide film.
Step five, preparing the graphene carbon film:
placing the reduced graphene oxide film in a hot-pressing reaction furnace, and carbonizing graphene by adopting a high-temperature vacuum heat treatment process; when the temperature is raised to 250 ℃, mechanical pressurization is carried out, and the pressure is 20 MPa; continuously heating to 1000 ℃, keeping the temperature for 2 hours, then cooling, and when the temperature is lowered to 250 ℃, removing the pressure; and continuously cooling to room temperature to obtain the graphene carbon film.
Step six, preparing a low-defect graphene film based on graphene foam:
placing the graphene carbon film in a high-temperature graphitization furnace, and adopting a gradient heating method to realize graphitization of the carbon film; heating to 1200 ℃ at a heating rate of 20 ℃/min, heating to 2200 ℃ at a heating rate of 10 ℃/min instead, keeping the temperature for 30min, heating to 2800 ℃ continuously at a heating rate of 5 ℃/min, keeping the temperature for 120min, and cooling to room temperature to obtain the low-defect graphene film based on the graphene foam.
In the embodiment, the thermal conductivity and the electric conductivity of the sample are tested to obtain the thermal conductivity of the low-defect graphene film based on the graphene foam of 950W m-1 K-1The conductivity reaches 1.05 multiplied by 105 S m-1Simultaneously, the low-defect graphene film based on the graphene foam prepared by the embodiment has higher tensile strength, reaches 66MPa, is compared with the existing graphene film which can exist independently, has low raw material cost, is uniformly dispersed in the prepared graphene, simultaneously has higher heat conduction and electric conduction performance and excellent mechanical strength, has certain flexibility, and meets the actual application requirements in the fields of national defense and military equipment and intelligent electronics.
Example 4:
in this embodiment, the preparation method of the low-defect graphene film based on the graphene foam is specifically performed according to the following steps:
step one, preparing a graphene oxide aqueous solution:
measuring 20mL of graphene oxide slurry with the concentration of 20mg/mL, and adding deionized water; stirring for 120min under the condition that the stirring speed is 100 r/min; and then, carrying out ultrasonic treatment for 60min under the condition that the frequency is 10KHz to obtain a graphene oxide aqueous solution with the graphene oxide concentration of 3 mg/mL.
Step two, preparing anisotropic graphene oxide frozen foam:
and (3) directionally freezing the graphene oxide aqueous solution by using liquid nitrogen to obtain anisotropic graphene oxide freezing foams with different shapes.
Step three, preparing anisotropic graphene oxide foam:
by using CO2And drying the anisotropic graphene oxide frozen foam by a supercritical drying method to obtain the anisotropic graphene oxide foam.
Step four, reducing the graphene oxide film:
placing the anisotropic graphene oxide composite foam in a hot-pressing reaction furnace, and reducing graphene oxide by adopting a hot-pressing oxidation pretreatment process; when the temperature is raised to 250 ℃, mechanical pressurization is carried out, and the pressure is 25 MPa; continuously heating to 350 ℃, keeping the temperature for 1.5h, then cooling, and when the temperature is as low as 250 ℃, removing the pressure; and continuously cooling to room temperature to obtain the reduced graphene oxide film.
Step five, preparing the graphene carbon film:
placing the reduced graphene oxide film in a hot-pressing reaction furnace, and carbonizing graphene by adopting a high-temperature vacuum heat treatment process; when the temperature is raised to 250 ℃, mechanical pressurization is carried out, and the pressure is 25 MPa; continuously heating to 800 ℃, keeping the temperature for 2.5 hours, then cooling, and when the temperature is as low as 250 ℃, removing the pressure; and continuously cooling to room temperature to obtain the graphene carbon film.
Step six, preparing a low-defect graphene film based on graphene foam:
placing the graphene carbon film in a high-temperature graphitization furnace, and adopting a gradient heating method to realize graphitization of the carbon film; heating to 1000 deg.C at a rate of 20 deg.C/min, heating to 2000 deg.C at a rate of 10 deg.C/min, and holding for 35 min; and changing the heating rate to 5 ℃/min, continuously heating to 3000 ℃, keeping the temperature for 115min, and then cooling to the room temperature to obtain the low-defect graphene film based on the graphene foam.
In the embodiment, the thermal conductivity and the electric conductivity of the sample are tested, so that the thermal conductivity of the low-defect graphene film based on the graphene foam is 1030W m-1 K-1The conductivity reaches 1.15 multiplied by 105 S m-1Simultaneously, the low-defect graphene film based on the graphene foam prepared by the embodiment has higher tensile strength, reaches 73MPa, is compared with the existing graphene film which can exist independently, has low raw material cost, is uniformly dispersed in the prepared graphene, simultaneously has higher heat conduction and electric conduction performance and excellent mechanical strength, has certain flexibility, and meets the actual application requirements in the fields of national defense and military equipment and intelligent electronics.
Example five:
in this embodiment, the preparation method of the low-defect graphene film based on the graphene foam is specifically performed according to the following steps:
step one, preparing a graphene oxide aqueous solution:
measuring 20mL of graphene oxide slurry with the concentration of 20mg/mL, and adding deionized water; stirring for 120min under the condition that the stirring speed is 100 r/min; and then, carrying out ultrasonic treatment for 60min under the condition that the frequency is 10KHz to obtain a graphene oxide aqueous solution with the graphene oxide concentration of 7 mg/mL.
Step two, preparing anisotropic graphene oxide frozen foam:
and (3) directionally freezing the graphene oxide aqueous solution by using liquid nitrogen to obtain anisotropic graphene oxide freezing foams with different shapes.
Step three, preparing anisotropic graphene oxide foam:
by using CO2And drying the anisotropic graphene oxide frozen foam by a supercritical drying method to obtain the anisotropic graphene oxide foam.
Step four, reducing the graphene oxide film:
placing the anisotropic graphene oxide composite foam in a hot-pressing reaction furnace, and reducing graphene oxide by adopting a hot-pressing oxidation pretreatment process; when the temperature is raised to 250 ℃, mechanical pressurization is carried out, and the pressure is 25 MPa; continuously heating to 350 ℃, keeping the temperature for 1.5h, then cooling, and when the temperature is as low as 250 ℃, removing the pressure; and continuously cooling to room temperature to obtain the reduced graphene oxide film.
Step five, preparing the graphene carbon film:
placing the reduced graphene oxide film in a hot-pressing reaction furnace, and carbonizing graphene by adopting a high-temperature vacuum heat treatment process; when the temperature is raised to 250 ℃, mechanical pressurization is carried out, and the pressure is 25 MPa; continuously heating to 800 ℃, keeping the temperature for 2.5 hours, then cooling, and when the temperature is as low as 250 ℃, removing the pressure; and continuously cooling to room temperature to obtain the graphene carbon film.
Step six, preparing a low-defect graphene film based on graphene foam:
placing the graphene carbon film in a high-temperature graphitization furnace, and adopting a gradient heating method to realize graphitization of the carbon film; heating to 1200 deg.C at a heating rate of 20 deg.C/min, heating to 2200 deg.C at a heating rate of 10 deg.C/min, and holding for 30 min; and changing the heating rate to 5 ℃/min, continuously heating to 2800 ℃, keeping the temperature for 120min, and then cooling to the room temperature to obtain the low-defect graphene film based on the graphene foam.
In the embodiment, by testing the thermal conductivity and the electric conductivity of the sample, the thermal conductivity of the low-defect graphene film based on the graphene foam is 970W m-1 K-1The conductivity reaches 1.0 multiplied by 105 S m-1Simultaneously, the low-defect graphene film based on the graphene foam prepared by the embodiment has higher tensile strength, reaches 69MPa, is compared with the existing graphene film which can exist independently, has low raw material cost, is uniformly dispersed in the prepared graphene, simultaneously has higher heat conduction and electric conduction performance and excellent mechanical strength, has certain flexibility, and meets the actual application requirements in the fields of national defense and military equipment and intelligent electronics.
Claims (6)
1. A preparation method of a low-defect graphene film based on graphene foam is characterized by comprising the following steps:
step one, preparing anisotropic graphene oxide frozen foam:
directionally freezing the graphene oxide aqueous solution by using liquid nitrogen to obtain anisotropic graphene oxide freezing foams with different shapes;
step two, preparing anisotropic graphene oxide foam:
by using CO2Drying the anisotropic graphene oxide frozen foam by a supercritical drying method to obtain anisotropic graphene oxide foam;
step three, reducing the graphene oxide film:
placing anisotropic graphene oxide foam in a hot-pressing reaction furnace, and reducing graphene oxide by adopting a hot-pressing oxidation pretreatment process, wherein the specific steps of reducing graphene oxide by adopting the hot-pressing oxidation pretreatment process are as follows: when the temperature is raised to 250 ℃, mechanical pressurization is carried out, and the pressure is controlled to be 20-30 MPa; continuously heating to 350-400 ℃, keeping the temperature for 1-1.5 h, then cooling, when the temperature is as low as 250 ℃, removing the pressure, and continuously cooling to room temperature to obtain a reduced graphene oxide film;
step four, preparing the graphene carbon film:
placing the reduced graphene oxide film in a hot-pressing reaction furnace, and implementing carbonization of graphene by adopting a high-temperature vacuum heat treatment process, wherein the specific steps of implementing carbonization of graphene by adopting the high-temperature vacuum heat treatment process are as follows: when the temperature is raised to 250 ℃, mechanical pressurization is carried out, and the pressure is controlled to be 20-30 MPa; continuously heating to 800-1000 ℃, keeping the temperature for 2-2.5 h, then cooling, when the temperature is as low as 250 ℃, removing the pressure, and continuously cooling to room temperature to obtain the graphene carbon film;
step five, preparing the low-defect graphene film based on the graphene foam:
placing a graphene carbon film in a high-temperature graphitization furnace, and adopting a gradient heating method to realize the graphitization of the carbon film, wherein the specific steps of adopting the gradient heating method to realize the graphitization of the carbon film are as follows: heating to 1000-1200 ℃ at a heating rate of 20 ℃/min, heating to 2000-2200 ℃ at a heating rate of 10 ℃/min instead, keeping the temperature for 30-35 min, heating to 2800-3000 ℃ at a heating rate of 5 ℃/min, keeping the temperature for 115-120 min, and cooling to room temperature to obtain the low-defect graphene film based on the graphene foam.
2. The preparation method of the graphene foam-based low-defect graphene film according to claim 1, wherein the preparation method of the graphene oxide aqueous solution is as follows: taking graphene oxide slurry as a raw material, adding deionized water, stirring for 60-120 min at a stirring speed of 100-700 r/min, and then carrying out ultrasonic treatment for 30-60 min at a frequency of 10-100 KHz to obtain a graphene oxide aqueous solution.
3. The preparation method of the graphene foam-based low-defect graphene film according to claim 1 or 2, wherein the concentration of graphene oxide in the graphene oxide aqueous solution is 1-10 mg/mL.
4. The preparation method of the graphene foam-based low-defect graphene film according to claim 3, wherein the concentration of the graphene oxide is 3-7 mg/mL.
5. The method for preparing a graphene foam-based low-defect graphene thin film according to claim 2, wherein the concentration of the graphene oxide slurry is 20 mg/mL.
6. The method for preparing a graphene foam-based low-defect graphene thin film according to claim 1, wherein the directional freezing is an ice separation induced self-assembly method.
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