CN109824033B - Method for preparing high-thermal-conductivity graphene film at low cost - Google Patents
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Abstract
The invention discloses a method for preparing high heat conductivity with low costMethods of graphene films. Dispersing graphite powder and potassium permanganate in concentrated sulfuric acid and phosphoric acid solution with the ratio of 7:1-11:1 to prepare graphite oxide suspension, washing and dispersing to obtain graphene oxide dispersion, and performing suction filtration at room temperature to prepare a graphene oxide film; placing the film in a high-temperature-resistant mold to obtain a primarily reduced graphene oxide film; and respectively soaking the primarily reduced graphene oxide film in one or more of glucose, fructose, sucrose and vitamin C solutions, heating to 800-1000 ℃, preserving heat for 50-70 minutes, and then gradually cooling to room temperature to obtain the graphene film with high thermal conductivity. The graphene film has the thickness of 10-50 microns and is controllable, and the room-temperature heat conductivity coefficient is 1050-‑1k‑1The tensile strength can reach 15-35MPa, and the product is not damaged after being bent for 100 times at 180 degrees.
Description
Technical Field
The invention relates to a graphene film, in particular to a method for preparing a high-thermal-conductivity graphene film at low cost, and the high-thermal-conductivity graphene film can be used in the fields of aviation, mobile equipment and the like.
Background
Most of traditional heat conduction materials are made of metal materials, have the defects of high mechanical strength, good heat resistance, high density, low heat conductivity, high manufacturing cost and the like, and are difficult to meet the requirements of people on production and life. The non-metallic materials, which are carbon materials represented by graphene, have excellent properties such as high thermal conductivity and corrosion resistance, and are hot research points of people. According to related reports, the highest thermal conductivity coefficient of the current graphene film with high thermal conductivity is 3200W m-1k-1The thermal conductivity coefficient of the graphene film prepared by adopting high-temperature hot-pressing reduction is generally 800-1800W m-1k-1The high-heat-conductivity graphite films sold in the market are basically subjected to high-temperature hot-pressing treatment, and the severe production conditions and high production cost limit the large-scale application of the high-heat-conductivity graphite films. And is prepared by adopting a low-temperature and low-pressure reduction process (the temperature is less than 2000 ℃)The prepared graphene film has strong damage of carbon dioxide released in the thermal stripping process to a lamellar structure, the obtained RGO lamellar structure has large defect degree, and the heat-conducting property and the mechanical property of the product can not meet the requirements of people. Therefore, on the premise of ensuring high thermal conductivity and high flexibility of the graphene film, reducing the production conditions and the production cost of the graphene film with high thermal conductivity is an important problem to be solved for large-scale application of the graphene film.
Graphene is the first two-dimensional atomic crystal synthesized and has received much attention because of its excellent range of properties. The graphene has high strength, rigidity and elasticity and good mechanical properties. In addition, the graphene has extremely high thermal conductivity and electron mobility, and the band gap is adjustable. A plurality of excellent properties are concentrated in one material, so that the material can replace other materials in a plurality of application occasions, and a series of technical breakthroughs are brought to related application fields. The graphene film as one of the macroscopic materials of graphene is particularly outstanding in heat conduction and heat transfer aspects by virtue of high heat conductivity coefficient, however, high-temperature hot-pressing treatment is generally adopted in the production process of the graphene film with high heat conductivity at present, the energy consumption in the production process is high, the energy conservation and emission reduction are not met, the requirement on production equipment is high, and the large-scale preparation of the graphene film is limited. Therefore, it is a development trend to research a production process which uses low temperature and low pressure and ensures higher heat conductivity and mechanical properties of the graphene film.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a room-temperature heat conduction coefficient of 1050--1k-1The method for preparing the high-thermal-conductivity graphene film at low cost has the tensile strength of 15-35MPa and no damage after 100-time 180-degree bending, and has the advantages of low preparation process temperature, low pressure, simplicity in operation, no pollution and low cost; the graphene film prepared by the invention only needs to be subjected to low-temperature and low-pressure thermal reduction treatment at the temperature of 800-1000 ℃ and 12-15MPa for 2 hours, while the high-heat-conductivity graphite film in the prior art needs to be subjected to high-temperature and high-pressure thermal reduction treatment at the temperature of 2800 ℃ and above 200MPa for 3 hours.
Preparing graphene oxide dispersion liquid by an improved Hummers method, and preparing a graphene oxide film by a solution film forming method; and after the graphene oxide film is subjected to primary hot-pressing reduction treatment, the graphene oxide film is respectively soaked in one or more solutions of glucose, fructose, sucrose and vitamin C, and finally the graphene oxide film is subjected to secondary hot-pressing reduction treatment to obtain the high-thermal-conductivity graphene film.
The purpose of the invention is realized by the following technical scheme:
a method for preparing a high-thermal-conductivity graphene film at low cost comprises the following steps:
1) oxidation treatment: dispersing graphite powder and potassium permanganate in concentrated sulfuric acid and phosphoric acid solution in a ratio of 7:1-11:1, stirring for 8-12 hours at 40-60 ℃, cooling to room temperature, and dropwise adding hydrogen peroxide under the conditions of ice water bath and stirring to remove residual potassium permanganate to obtain bright yellow graphite oxide suspension;
2) washing and dispersing: standing and layering the graphite oxide suspension, pouring out supernatant, and dropwise adding dilute hydrochloric acid into the graphite oxide precipitate; standing, layering, pouring out supernatant, adding dilute hydrochloric acid into the precipitate, repeatedly washing, adding deionized water into the last graphite oxide precipitate, centrifuging, pouring out centrifugal supernatant, adding deionized water into the rest graphite oxide precipitate, ultrasonically dispersing for 2-4 hours, then filling into a dialysis bag, and dialyzing for several days in deionized water until sulfate ions are not detected in the dialyzed deionized water and the pH value is 6.5-7.0 to obtain a graphene oxide dispersion liquid;
3) carrying out suction filtration on the graphene oxide dispersion liquid at room temperature to prepare a graphene oxide film;
4) placing the graphene oxide film in a high-temperature-resistant mold, heating to 300-400 ℃, and gradually cooling to room temperature after heat preservation for 50-70 minutes in an inert atmosphere to obtain a primarily reduced graphene oxide film;
5) respectively soaking the primarily reduced graphene oxide film in one or more of glucose, fructose, sucrose and vitamin C solutions, then heating the soaked graphene oxide film to 800-.
In order to further achieve the purpose of the invention, preferably, the mass ratio of the graphite powder, the concentrated sulfuric acid and the potassium permanganate is 1:60-70: 3-6.
Preferably, the molar concentration of the concentrated sulfuric acid is 15-18mol L-1The molar concentration of the concentrated phosphoric acid is 16-19mol L-1The molar concentration of the dilute hydrochloric acid is 2.0-3.0mol L-1。
Preferably, the number of washing repetitions is from 4 to 6; the rotation speed of the centrifugal treatment is 4000-6000rpm, and the time is 2-4 hours.
Preferably, the graphene oxide film in the step 3) has a diameter of 40-50mm and a thickness of 10-50 microns; the suction filtration time in the step 3) is 8-12 h; and 2) the concentration of the graphene oxide dispersion liquid in the step 2) is 1.0-8.0mg/mL, and no precipitate is generated after the graphene oxide dispersion liquid is stably stored for more than 6 months.
Preferably, the concentration of the solution of one or more of glucose, fructose, sucrose and vitamin C of step 5) is 1-5 mg/mL.
Preferably, the step 4) is performed in a high-temperature tube furnace or graphitization furnace in an inert gas atmosphere: the inert gas comprises argon or nitrogen.
Preferably, the graphene oxide dispersion liquid is further dried after being subjected to suction filtration at room temperature, and the drying is vacuum drying.
Preferably, the step of heating the soaked graphene oxide film is performed by placing the soaked graphene oxide film in a boat; the high-temperature resistant mold is a graphite mold.
Preferably, the thickness of the graphene film with high thermal conductivity is 10-50 microns and is controllable, and the room-temperature heat conductivity coefficient is 1050-1550W m-1k-1The tensile strength is 15-35MPa, and the steel pipe is not damaged after being bent for 100 times at 180 degrees.
Compared with the prior art, the invention has the following advantages and beneficial effects:
(1) the improved Hummers method used in the invention does not need to use harmful nitrates (such as sodium nitrate and the like) to prepare the graphene oxide dispersion liquid; the graphene oxide dispersion liquid is prepared by a one-step oxidation method, and the preparation method is simple to operate and easy to prepare; the prepared graphene oxide dispersion liquid can be stably stored for more than 6 months without sediment, a large number of graphene oxide nanosheets containing oxygen functional groups interact with each other and the graphene oxide nanosheets and water molecules, the uniform dispersion of graphene oxide sheets can be effectively maintained, and sufficient raw material guarantee is provided for the subsequent preparation of a graphene film.
(2) The thickness of the graphene film prepared by the method is 10-50 microns and controllable, and the heat conductivity coefficient is 1050-1550W m below room temperature-1k-1The tensile strength is 15-35MPa, the sheet is not damaged by 100-time 180-degree cyclic bending or folding, no obvious powder falling is caused, and the sheet has good heat transfer performance and mechanical performance. Most of the commercialized graphene films (such as PGS graphene film under Pinus koraiensis, carbon element technology graphene film in Henzhou, etc.) are processed at 2800 ℃ and 200MPa or more, and when the film thickness is 40 micrometers, the thermal conductivity coefficient is 1100-1300W m-1k-1And the tensile strength is 20-25 MPa. The invention can obtain the thermal conductivity 1053W m only by processing at the temperature of 800--1k-1Graphene film with tensile strength of 19 MPa. Compared with the current commercialized graphene film, the thermal conductivity and mechanical property of the product are slightly reduced, but the product can completely meet the production and living needs of people for the high thermal conductivity graphene film, the production process is simple, the requirements on equipment are obviously reduced, the energy consumption is less and greatly reduced, the prepared graphene film only needs to be subjected to 2-hour low-temperature low-pressure thermal reduction treatment at the temperature of 800-1000 ℃ and 12-15MPa, and the high thermal conductivity graphite film sold in the market is basically subjected to more than 2-hour high-temperature high-pressure thermal reduction treatment at the temperature of 2800 ℃ and 200MPa, so the production cost of the graphene film produced by the product is greatly reduced.
(3) According to the invention, the secondary hot-pressing reduction process is adopted, most of oxygen-containing groups in the graphene oxide membrane can be removed under the conditions of low temperature (300-. Compared with the prior art, the method for preparing the commercial graphite film or the graphene film under the high temperature (2000-.
(4) The graphene oxide membrane prepared by the invention is respectively soaked in one or more solutions of glucose, fructose, sucrose and vitamin C after being subjected to one-time hot pressing treatment, one or more molecules of glucose, fructose, sucrose and vitamin C which permeate into the graphene oxide membrane after being soaked for a long time are decomposed by heat treatment at 1000 ℃ of 800-. The repaired graphene film has a more complete lamellar structure, a heat conduction channel is more smooth, phonon scattering is reduced, and the overall heat conduction performance and mechanical performance of the graphene film are improved.
Drawings
FIG. 1 is a graph of the effect of GO dispersions of different concentrations prepared in step 1) of example 1 after 1 day storage;
FIG. 2 is a graph of the effect of GO dispersions of different concentrations prepared in step 1) of example 1 after 180 days of storage;
FIG. 3 is an SEM image of the graphene film obtained in step 4) of example 1 before repair;
FIG. 4 is an SEM image of the graphene film obtained after step 4) repair in example 1;
FIG. 5 is a TEM image of the graphene film before step 4) repair of example 1;
fig. 6 is a TEM image of the graphene film after the step 4) repair of example 1.
Detailed Description
The present invention is further described with reference to the following examples, which should not be construed as limiting the scope of the present invention, but rather as providing those skilled in the art with insubstantial changes and modifications from the invention.
Prepared film sampleThe thermal conductivity of the product was calculated by the formula λ ═ α · ρ · Cp, where λ is the thermal conductivity of the sample (W m)-1k-1) And alpha is the thermal diffusivity (mm) of the sample2s-1) And ρ is the density of the sample (g cm)-3) Cp is the specific heat capacity of the sample (J g)-1K-1) (ii) a Furthermore, the sample is measured by adopting a laser flash method with rapid and accurate characteristics facing to the thermal diffusion coefficient, the used instrument is a flash method thermal conductivity instrument (NETZSCH LFA 447 NanoFlas), and the measurement temperature is room temperature; the density of the sample is calculated by the mass and the volume of the sample; the specific heat capacity of the sample was measured by a dynamic flow differential scanning calorimeter (DSC, NETZSCH DSC 204F1) at a test temperature of 25 ℃. Film samples were oriented to specific test procedure references for thermal conductivity (Kong, Qing-Qiang, Liu Z, Gao, Jian-Guo, et al, historical graphics-Carbon Fiber Composite Paper as a Flexible Heat radiator [ J]Advanced Functional Materials,2014,24(27): 4222-; preparation of Song-Ning-Jing-graphene-based thin film and mechanical and thermal property research [ D]University of chinese academy of sciences, 2016).
The tensile strength refers to the resistance of the maximum uniform plastic deformation which can be borne by the material, and is used for judging the mechanical property of the material. The tensile strength of the sample was measured using a dynamic thermomechanical analyzer (TA DMA Q800) with a 0.01N pre-stress and a 0.05% min tensile rate-1. The tensile strength test of the graphene film sample refers to the Chinese standard number: ASTM F152-1995 (R2017).
And (3) bending test, namely directly bending the film sample for 100 times at 180 degrees under the unsupported condition, wherein the minimum curvature radius can reach 4.0 mm, and no damage occurs.
Example 1
A method for repairing defects of a graphene film comprises the following specific steps:
(1) preparation of graphene oxide dispersions by modified Hummers method
Oxidation treatment: 180mL of concentrated sulfuric acid and 20mL of concentrated phosphoric acid are mixed, the reaction system is kept at 35 ℃, and 2.0g of graphite powder and 10g of potassium permanganate are added. Then keeping the temperature of the reaction solution at 50 ℃, stirring for 12 hours, adding 200 mL of deionized water, and dropwise adding 5mL of 30% hydrogen peroxide solution under an ice bath condition to remove residual potassium permanganate to obtain a graphene oxide suspension liquid with bright yellow solution;
washing and dispersing: standing and layering the obtained graphene oxide suspension, carefully pouring out supernatant, and adding 100 ml of 2.0mol L into precipitate-1HCl, standing again for layering, pouring out supernatant, and adding 100 ml of 2.0mol L-1And (3) repeating HCl for 3 times, adding 100 ml of deionized water into the last graphite oxide precipitate, centrifuging for 4 hours at 4000rpm, pouring out the supernatant, adding 150 ml of deionized water into the rest graphite oxide precipitate, ultrasonically dispersing for 3 hours, then filling into a dialysis bag, and dialyzing for 7 days in deionized water until sulfate ions are not detected in the dialyzed deionized water and the pH value is 7.0 to obtain the graphene oxide dispersion liquid. The prepared graphene oxide dispersion liquid has good water dispersibility, the concentration of the graphene oxide dispersion liquid after dilution can reach 1-6mg/ml, and the graphene oxide dispersion liquid is stably stored for 6 months without agglomeration/precipitation. The effect diagrams of the diluted GO dispersion liquid with different concentrations after being stored for 1 day and 180 days are shown in fig. 1 and fig. 2, which illustrate that a large number of graphene oxide nanosheets with oxygen-containing functional groups exist, the graphene oxide nanosheets and water molecules interact with each other, the graphene oxide nanosheets can be effectively maintained to be uniformly dispersed, and the graphene oxide dispersion liquid after being stored for a long time does not have agglomeration/precipitation.
(2) Vacuum filtering the uniformly mixed graphene oxide dispersion liquid on a mixed cellulose filter membrane (Jinteng, water system filter membrane) with the diameter of 50mm and the pore diameter of 45 microns for 6 hours by adopting a vacuum filtration method, taking the filter membrane out, putting the filter membrane in a vacuum drying oven at 50 ℃ for drying for 2 hours, and tearing off the mixed cellulose filter membrane to obtain the graphene oxide-based composite film;
(3) placing the graphene oxide film in a graphite mold, applying 3MPa pressure, heating to 350 ℃ in a high-temperature tube furnace protected by argon atmosphere, preserving heat for 60 minutes, and then gradually cooling to room temperature to obtain a primarily reduced graphene oxide film;
(4) placing the primarily reduced graphene oxide film in a 1.5mg/mL glucose solution for soaking for five days, then placing the film in a vacuum drying oven for drying for 2 hours, then taking down the film, placing the film in a boat, applying 13MPa pressure, heating the film to 1000 ℃ in a graphitization furnace protected by argon atmosphere, preserving heat for 3 hours, then gradually cooling the film to room temperature, and obtaining the graphene film with high thermal conductivity through roll pressing treatment.
Pictures of the graphene film before and after repair are shown in fig. 3 and 4 through a Scanning Electron Microscope (SEM), and it can be seen from fig. 3 that the graphene film before repair has more faults in the surface and a heat conduction channel is not smooth; fig. 4 shows that the repaired graphene film has orderly arranged inner sheets, fewer discontinuous layers, smoother overall heat conduction channel and faster heat conduction speed.
As shown in fig. 5 and 6, a Transmission Electron Microscope (TEM) of the graphene film before and after the repair is shown, and it can be seen from fig. 5 that the domain area of the thin film is small and the roughness is large; corresponding TEM characterization fig. 5 shows that the lattice fringes are arranged more disorderly and discontinuously, and more scattering occurs during phonon transmission. And fig. 6 shows that the crystal domain area of the C-Gr film improved by adding glucose is obviously increased, the roughness is small, and the corresponding TEM representation fig. 5 shows that the film has obvious lattice stripes and is arranged orderly, which indicates that the glucose can effectively repair the defects of the graphene nanosheets, increase the crystal domain area of the sheet, and improve the heat conduction channel of the microstructure of the film to make the film more complete.
The repaired graphene film has a more complete lamellar structure, a heat conduction channel is more smooth, phonon scattering is reduced, and the overall heat conduction performance and mechanical performance of the graphene film are improved.
The graphene film obtained in the embodiment has the thickness of 16 microns and the facing thermal conductivity of 1530W m through testing-1k-1The tensile strength is 30MPa, and the steel plate is not damaged after being bent for 100 times at 180 degrees.
The Thermal conductivity and mechanical properties of the material prepared in this example are comparable to those of the prior art (reference: Peng L, Xu Z, Liu Z, et al. ultra high Thermal Conductive layer Superflexible Graphene Films [ J].Advanced Materials,2017,29(27)；Ding J,Rahman O U,Zhao H,et al.Hydroxylated graphene-based flexible carbon film with ultrahigh electrical and thermal conductivity[J].Nanotechnology,2017,28.)In contrast, the graphene film prepared in this example has a thickness of 16 microns and a thermal conductivity of 1530W m-1k-1The tensile strength is 30 MPa; the graphene film prepared by the prior art has the facing thermal conductivity of 1700W m when the thickness is 17 microns-1k-1The tensile strength was 38 MPa. Compared with the product, the thermal conductivity difference is only 170W m-1k-1The tensile strength difference was only 9 MPa. Although the thermal conductivity of commercial heat-conducting film materials is generally required to be higher and better, the thermal conductivity can reach 800W m-1k-1The above heat-conducting film material can basically meet the requirements of people. The graphene film with high thermal conductivity can be used in the fields of aviation, mobile equipment and the like, for example, a mobile phone named as Mate 20X was introduced to the company hua 2018, the mobile phone adopts the graphene heat dissipation film as the heat dissipation film, the heat dissipation surface made of graphene is used, and the heat dissipation effect of the graphene heat dissipation film is far better than that of carbon nano tubes, metal nano particles and other fillers. The production process of the product is simple, the requirement on equipment is obviously reduced (high-temperature production equipment heated to 3000 ℃ is not needed, only production equipment heated to 1000 ℃) is needed, the energy consumption is less, the prepared graphene film only needs to be subjected to low-temperature low-pressure thermal reduction treatment for 2 hours at the temperature of 800-1000 ℃ and 12-15MPa, and the high-thermal-conductivity graphite film sold in the market is basically subjected to high-temperature high-pressure thermal reduction treatment for more than 2 hours at the temperature of 2800 ℃ and 200MPa, so that the production cost of the graphene film is obviously reduced by the process for producing the graphene film by the product.
Example 2
(1) Preparation of graphene oxide dispersions by modified Hummers method
Oxidation treatment: 180mL of concentrated sulfuric acid and 20mL of concentrated phosphoric acid are mixed, the reaction system is kept at 35 ℃, and 1.5g of graphite powder and 9g of potassium permanganate are added. Then keeping the temperature of the reaction solution at 50 ℃, stirring for 12 hours, adding 200 mL of deionized water, and dropwise adding 5mL of 30% hydrogen peroxide solution under an ice bath condition to remove residual potassium permanganate to obtain a graphene oxide suspension liquid with bright yellow solution;
washing and dispersing: standing and layering the obtained graphene oxide suspension, carefully pouring out supernatant, and addingAdding 3.0mol L of 100 ml into the precipitate-1HCl, standing again for layering, pouring out supernatant, and adding 100 ml of 3.0mol L-1And (3) repeating HCl for 3 times, adding 100 ml of deionized water into the last graphite oxide precipitate, centrifuging for 4 hours at 4000rpm, pouring out the supernatant, adding 150 ml of deionized water into the rest graphite oxide precipitate, ultrasonically dispersing for 3 hours, then filling into a dialysis bag, and dialyzing for 7 days in deionized water until sulfate ions are not detected in the dialyzed deionized water and the pH value is 7.0 to obtain the graphene oxide dispersion liquid. The prepared graphene oxide dispersion liquid has good water dispersibility, the concentration of the graphene oxide dispersion liquid after dilution can reach 1-6mg/ml, and the graphene oxide dispersion liquid is stably stored for 6 months without agglomeration/precipitation. The effect diagrams of the diluted GO dispersion liquid with different concentrations after being stored for 1 day and 180 days are shown in fig. 1 and fig. 2, which illustrate that a large number of graphene oxide nanosheets with oxygen-containing functional groups exist, the graphene oxide nanosheets and water molecules interact with each other, the graphene oxide nanosheets can be effectively maintained to be uniformly dispersed, and the graphene oxide dispersion liquid after being stored for a long time does not have agglomeration/precipitation.
(2) Vacuum filtering the uniformly mixed graphene oxide dispersion liquid on a mixed cellulose filter membrane (Jinteng, water system filter membrane) with the diameter of 50mm and the pore diameter of 45 microns for 6 hours by adopting a vacuum filtration method, taking the filter membrane out, putting the filter membrane in a vacuum drying oven at 50 ℃ for drying for 2 hours, and tearing off the mixed cellulose filter membrane to obtain the graphene oxide membrane;
(3) placing the graphene oxide film in a graphite mold, applying 3MPa pressure, heating to 350 ℃ in a high-temperature tube furnace protected by argon atmosphere, preserving heat for 1 hour, and then gradually cooling to room temperature to obtain a primarily reduced graphene oxide film;
(4) placing the preliminarily reduced graphene oxide film in a 1.5mg/mL glucose solution, heating the solution to 80 ℃, keeping the temperature unchanged, and soaking for 12 hours. And taking out the soaked film, drying the film for 2 hours in a vacuum drying oven, taking down the film, placing the graphene oxide film in a boat, applying a pressure of 13MPa, heating the film to 1000 ℃ in a graphitization furnace protected by argon atmosphere, preserving the heat for 3 hours, gradually cooling the film to room temperature, and carrying out roll-pressing treatment to obtain the graphene film with high heat conductivity. The graphene films before and after repair were similar to fig. 3 and 4 by Scanning Electron Microscopy (SEM); transmission Electron Microscopy (TEM) of the graphene films before and after repair is similar to fig. 5 and 6. The repaired graphene film has a more complete lamellar structure, a heat conduction channel is more smooth, phonon scattering is reduced, and the overall heat conduction performance and mechanical performance of the graphene film are improved.
The graphene film of the embodiment is tested to be 25 microns thick and 1230W m in thermal conductivity-1k-1The tensile strength is 24MPa, and the steel plate is not damaged after being bent for 100 times at 180 degrees.
Example 3
(1) Preparation of graphene oxide dispersions by an improved Hummers method
Oxidation treatment: 180mL of concentrated sulfuric acid and 20mL of concentrated phosphoric acid are mixed, the reaction system is kept at 35 ℃, and 1.5g of graphite powder and 10g of potassium permanganate are added. Then keeping the temperature of the reaction solution at 50 ℃, stirring for 12 hours, adding 200 mL of deionized water, and dropwise adding 5mL of 30% hydrogen peroxide solution under an ice bath condition to remove residual potassium permanganate to obtain a graphene oxide suspension liquid with bright yellow solution;
washing and dispersing: standing and layering the obtained graphene oxide suspension, carefully pouring out supernatant, and adding 100 ml of 2.5mol L into the precipitate-1HCl, standing again for layering, pouring out supernatant, and adding 100 ml of 2.5mol L-1And (3) repeating HCl for 3 times, adding 100 ml of deionized water into the last graphite oxide precipitate, centrifuging for 4 hours at 4000rpm, pouring out the supernatant, adding 150 ml of deionized water into the rest graphite oxide precipitate, ultrasonically dispersing for 3 hours, then filling into a dialysis bag, and dialyzing for 7 days in deionized water until sulfate ions are not detected in the dialyzed deionized water and the pH value is 7.0 to obtain the graphene oxide dispersion liquid. The prepared graphene oxide dispersion liquid has good water dispersibility, the concentration of the graphene oxide dispersion liquid after dilution can reach 1-6mg/ml, and the graphene oxide dispersion liquid is stably stored for 6 months without agglomeration/precipitation. Effect of GO dispersions of different concentrations prepared after dilution after storage for 1 and 180 days are shown in FIGS. 1 and 2, illustrating the presence of a large amount ofThe graphene oxide nanosheets containing oxygen functional groups interact with each other and the graphene oxide nanosheets and water molecules, so that the graphene oxide nanosheets can be effectively maintained to be uniformly dispersed, and the graphene oxide dispersion liquid after long-time storage is free from agglomeration/precipitation.
(2) Vacuum filtering the uniformly mixed graphene oxide dispersion liquid on a mixed cellulose filter membrane (Jinteng, water system filter membrane) with the diameter of 50mm and the pore diameter of 45 microns for 6 hours by adopting a vacuum filtration method, taking the filter membrane out, putting the filter membrane in a vacuum drying oven at 50 ℃ for drying for 2 hours, and tearing off the mixed cellulose filter membrane to obtain the graphene oxide film;
(3) placing the graphene oxide film in a graphite mold, applying 3MPa pressure, heating to 350 ℃ in a high-temperature tube furnace protected by argon atmosphere, preserving heat for 1 hour, and then gradually cooling to room temperature to obtain a primarily reduced graphene oxide film;
(4) placing the primarily reduced graphene oxide film in a 1:1 mixed glucose and vitamin C mixed solution with the concentration of 1.5mg/mL, soaking for five days, then drying in a vacuum drying oven for 2 hours, then taking down the graphene oxide film, placing the graphene oxide film in a boat, applying the pressure of 10MPa, heating to 1000 ℃ in a graphitization furnace protected by argon atmosphere, preserving the temperature for 3 hours, then gradually cooling to room temperature, and carrying out roll pressing treatment to obtain the graphene film with high thermal conductivity. The graphene films before and after repair were similar to fig. 3 and 4 by Scanning Electron Microscopy (SEM); transmission Electron Microscopy (TEM) of the graphene films before and after repair is similar to fig. 5 and 6. The repaired graphene film has a more complete lamellar structure, a heat conduction channel is more smooth, phonon scattering is reduced, and the overall heat conduction performance and mechanical performance of the graphene film are improved.
Through tests, the graphene-based composite film of the embodiment has the thickness of 39 micrometers and the facing thermal conductivity of 1053W m-1k-1The tensile strength is 19MPa, and the steel pipe is not damaged after being bent for 100 times at 180 degrees.
The existing high Thermal conductivity Graphene film is prepared by adopting high temperature (2000-. The Graphene film prepared by adopting the traditional low-temperature low-pressure reduction process (the temperature is less than 2000 ℃) has stronger damage to a lamellar structure by carbon dioxide released in the Thermal stripping process, the structural defect degree of the obtained RGO lamellar is larger, and the Thermal conductivity and the mechanical property are generally 220-390W/mK and 10-15MPa, and can not meet the requirements of people on the Graphene film (the reference documents are Hou Z L, Song W L, Wang P, et al.
The method for reducing the production cost of the high-thermal-conductivity graphene film has the characteristics of low temperature, low pressure and low energy consumption, effectively repairs the defects of the graphene film, effectively improves the thermal conductivity of the unrepaired graphene film (the thermal conductivity of the unrepaired graphene film is 500-690W/mK) compared with the unrepaired graphene film, and basically meets the performance requirements of people on the high-thermal-conductivity material.
Compared with the process temperature of 2500-; the low pressure is 2-5MPa and 12-15MPa, and compared with the prior art that the process pressure is 200-300MPa, the low pressure has the advantages of obviously lower pressure, low requirement on equipment and reduction of production cost; the invention has the advantages of low temperature, low pressure and low energy consumption, so that on one hand, the production condition is milder, the harsh condition requirement of the used equipment is less, the safe and reliable performance of the operation is higher, the operation is simpler and more convenient, and the production cost is greatly reduced; on the other hand, the defects of the graphene film are repaired by carbon atoms generated by thermal decomposition of one or more molecules of glucose, fructose, sucrose and vitamin C, and the graphene film (with the thermal conductivity coefficient of 500-700W m) obtained without soaking in one or more solutions of glucose, fructose, sucrose and vitamin C is obtained-1k-1Tensile strength of 10-20 MPa), and heat conductivityAnd the tensile strength is effectively improved by 110-120% and 50-75% respectively, and the requirements of people on the performance of high-heat-conduction materials are met.
The existing high-thermal-conductivity graphene film is generally subjected to high-temperature high-pressure treatment at 3000 ℃ of 2000--1k-1The tensile strength is 10-40 MPa, the production process has high requirements on equipment, the energy consumption is high, and the production cost is high.
The graphene film prepared by the method only needs to be processed at a lower temperature (1000 ℃) and a lower pressure (12-15MPa) to obtain the graphene film with excellent performance, the thickness of the graphene film is 10-50 microns and controllable, and the heat conductivity coefficient in a room temperature plane is 1050-1550W m-1k-1The tensile strength can reach 15-35MPa, the product is not damaged after being bent for 100 times at 180 degrees, the production process has lower requirements on equipment, the energy consumption is less, and the production cost is low. The Thermal conductivity and the mechanical property of the material prepared by the invention are the same as those of the prior art (reference document: Peng L, Xu Z, Liu Z, et al].Advanced Materials,2017,29(27)；Ding J,Rahman O U,Zhao H,et al.Hydroxylated graphene-based flexible carbon film with ultrahigh electrical and thermal conductivity[J]Nanotechnology,2017,28.) the graphene film produced was 16 microns thick and had a thermal conductivity facing 1530W m-1k-1The tensile strength is 30 MPa; the graphene film prepared by the prior art has the facing thermal conductivity of 1700W m when the thickness is 17 microns-1k-1The tensile strength was 38 MPa. Compared with the product, the thermal conductivity difference is only 170W m-1k-1The tensile strength difference was only 9 MPa. Although the thermal conductivity of commercial heat-conducting film materials is generally required to be higher and better, the thermal conductivity can reach 800W m-1k-1The above heat-conducting film material can basically meet the requirements of people. The product has simple production process, obviously reduces the requirement on equipment (only production equipment heated to 1000 ℃ is needed instead of high-temperature production equipment heated to 3000 ℃), has less energy consumption and greatly reduces the energy consumption, and the prepared graphene film only needs to be 800-plus-material after 2 hoursThe graphene film is subjected to low-temperature and low-pressure thermal reduction treatment at 1000 ℃ and 12-15MPa, and the high-thermal-conductivity graphite film sold in the market is subjected to high-temperature and high-pressure thermal reduction treatment at 2800 ℃ and 200MPa for more than 2 hours, so that the process for producing the graphene film by using the product remarkably reduces the production cost of the graphene film.
Compared with the prior art, the graphene film has excellent comprehensive performance, although the heat conductivity coefficient and the tensile strength are slightly lower than those of the graphene film in the prior art, the graphene film basically meets the performance requirements of people on the graphene film, more importantly, the flexible and light graphene film with high heat conductivity is prepared under mild process conditions, is more energy-saving and lower in cost, has a wide application range, and has great application prospects in the fields of high-power and high-heat-flow-density electronic industry and heat dissipation of electronic devices of intelligent equipment.
Claims (8)
1. A method for preparing a high-thermal-conductivity graphene film at low cost is characterized by comprising the following steps:
1) oxidation treatment: dispersing graphite powder and potassium permanganate in concentrated sulfuric acid and phosphoric acid solution in a ratio of 7:1-11:1, stirring for 8-12 hours at 40-60 ℃, cooling to room temperature, and dropwise adding hydrogen peroxide under the conditions of ice water bath and stirring to remove residual potassium permanganate to obtain bright yellow graphite oxide suspension; the mass ratio of the graphite powder to the concentrated sulfuric acid to the potassium permanganate is 1:60-70: 3-6;
2) washing and dispersing: standing and layering the graphite oxide suspension, pouring out supernatant, and dropwise adding dilute hydrochloric acid into the graphite oxide precipitate; standing, layering, pouring out supernatant, adding dilute hydrochloric acid into the precipitate, repeatedly washing, adding deionized water into the last graphite oxide precipitate, centrifuging, pouring out centrifugal supernatant, adding deionized water into the rest graphite oxide precipitate, ultrasonically dispersing for 2-4 hours, then filling into a dialysis bag, and dialyzing for several days in deionized water until sulfate ions are not detected in the dialyzed deionized water and the pH value is 6.5-7.0 to obtain graphene oxide dispersion liquid;
3) carrying out suction filtration on the graphene oxide dispersion liquid at room temperature to prepare a graphene oxide film;
4) placing the graphene oxide film in a high-temperature-resistant mold, heating to 300-400 ℃, and gradually cooling to room temperature after heat preservation for 50-70 minutes in an inert atmosphere to obtain a primarily reduced graphene oxide film;
5) respectively soaking the primarily reduced graphene oxide film in one or more solutions of glucose, fructose, sucrose and vitamin C, then heating the soaked graphene oxide film to 800-; the thickness of the graphene film with high thermal conductivity is 10-50 micrometers, the room-temperature heat conductivity coefficient is 1050-1550W/(m.K), the tensile strength is 15-35MPa, and the graphene film is free of damage after being bent for 100 times at 180 degrees.
2. The method for preparing the graphene film with high thermal conductivity at low cost according to claim 1, wherein: the molar concentration of the concentrated sulfuric acid is 15-18 mol/L, the molar concentration of the phosphoric acid is 16-19 mol/L, and the molar concentration of the dilute hydrochloric acid is 2.0-3.0 mol/L.
3. The method for preparing the graphene film with high thermal conductivity at low cost according to claim 1, wherein: the repeated washing times are 4-6 times; the rotation speed of the centrifugal treatment is 4000-6000rpm, and the time is 2-4 hours.
4. The method for preparing the graphene film with high thermal conductivity at low cost according to claim 1, wherein: the graphene oxide film in the step 3) has the diameter of 40-50mm and the thickness of 10-50 microns; the suction filtration time in the step 3) is 8-12 h; and 2) the concentration of the graphene oxide dispersion liquid in the step 2) is 1.0-8.0mg/mL, and no precipitate is generated after the graphene oxide dispersion liquid is stably stored for more than 6 months.
5. The method for preparing the graphene film with high thermal conductivity at low cost according to claim 1, wherein: and step 5) the concentration of one or more of glucose, fructose, sucrose and vitamin C solution is 1-5 mg/mL.
6. The method for preparing the graphene film with high thermal conductivity at low cost according to claim 1, wherein: the step 4) is a high-temperature tube furnace or a graphitization furnace in an inert gas atmosphere: the inert gas comprises argon or nitrogen.
7. The method for preparing the graphene film with high thermal conductivity at low cost according to claim 1, wherein: the graphene oxide dispersion liquid is subjected to suction filtration at room temperature and then is dried, wherein the drying is vacuum drying.
8. The method for preparing the graphene film with high thermal conductivity at low cost according to claim 1, wherein: the step of heating the soaked graphene oxide film is carried out by placing the soaked graphene oxide film in a boat; the high-temperature resistant mold is a graphite mold.
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