A method for preparing reduced graphene oxide film based on electrohydrodynamic atomization inkjet printing

Abstract

The application discloses a method for preparing a reduced graphene oxide film based on electrohydrodynamic atomization jet printing, which comprises the following steps: (1) obtaining an oxidized graphene liquid film on the surface of a substrate by electrohydrodynamic atomization jet printing of an oxidized graphene precursor solution; (2) drying the oxidized graphene liquid film to obtain an oxidized graphene dry film; and (3) obtaining a reduced graphene oxide film by chemical reduction of the oxidized graphene dry film; wherein the oxidized graphene precursor solution is a mixed solution of an oxidized graphene suspension and an organic solvent; and the oxidized graphene suspension is a deionized water phase suspension. The specific oxidized graphene precursor solution adopted in the application meets the conditions of electrohydrodynamic atomization jet printing and promotes the self-assembly of oxidized graphene nanosheets, so that large-scale preparation of a high-performance reduced graphene oxide film is finally realized.

Description

Technical Field

[0001] This invention relates to the field of two-dimensional material thin film preparation technology, and in particular to a method for preparing reduced graphene oxide films based on electrofluid atomization printing. Background Technology

[0002] In recent years, two-dimensional (2D) van der Waals (vdW) layered materials, including graphene, transition metal dihydrides (TMD), hexagonal boron nitride (h-BN), and MXenes, have attracted widespread attention due to their unique physicochemical properties. Typically, the lateral dimensions of vdW materials are limited to only tens of micrometers, restricting their applications. Therefore, there is an urgent need to develop processes for the large-scale synthesis of high-performance 2D vdW materials.

[0003] Graphene has broad application prospects in fields such as electronics, defense, healthcare, and energy. However, it has not yet achieved true commercialization. Currently, all commercially available graphene films are prepared by chemical vapor deposition (CVD). CVD preparation of graphene films is complex, requiring high-temperature and high-pressure environments, and is also costly and difficult to transfer.

[0004] Graphene oxide (GO) nanosheets have been proven to be a universal two-dimensional building block for various macroscopic structures, such as films or fibers. The performance of high-quality reduced monolayer graphene oxide films can approach that of graphene films prepared by CVD. However, to fully utilize the properties of graphene oxide, ensuring the alignment and orientation of graphene oxide nanosheets is crucial for preparing high-quality reduced graphene oxide films. Traditional methods for preparing graphene oxide films, such as vacuum filtration (VF), interfacial assembly, Langmuir-Blodgett assembly, and gel-film conversion (GFT), struggle to control the assembly process of graphene oxide nanosheets. This results in films with nanoscale thicknesses that are difficult to achieve, exhibiting poor performance and low quality, thus limiting their large-scale application.

[0005] Electrofluidic inkjet printing, as an emerging micro- and nanoscale processing technology, can be used to produce functional materials with micro- and nanoscale structural features. The principle of electrofluidic inkjet printing is to spray extremely small droplets from the tip of a Taylor cone under the drive of a spatial electric field. It has three modes: electrofluidic spot spraying, electrofluidic spinning, and electrofluidic atomization. Different printing modes can be achieved depending on the properties of the precursor solution. Among them, electrofluidic atomization inkjet printing has the characteristics of small droplets (nanoscale), large area, and uniformity, making it suitable for preparing micro- and nanoscale thin film materials.

[0006] The most important aspect of preparing high-performance two-dimensional material films using two-dimensional nanomaterials is controlling the film thickness and surface roughness. Existing technologies, such as the SN201807129 electro-inking equipment from Wuhan Huawike Intelligent Technology Co., Ltd., disclose its applicability to graphene, but the film thickness prepared by their equipment exceeds 50 nm, and the resulting graphene film has a large surface roughness and poor performance.

[0007] Electrofluidic atomization printing, in principle, can be used to prepare large-area, high-quality two-dimensional material films; however, it presents certain difficulties in practical operation. The applicant previously discovered that the key to preparing high-quality film materials using electrofluidic printing is the precursor solution. For graphene materials, preparing films using electrofluidic printing equipment requires preparing the two-dimensional nanomaterials into a liquid suspension. However, existing methods often produce graphene suspensions that are prone to precipitation, or graphene oxide suspensions that cannot be directly used for electrofluidic atomization printing, or the suspensions cannot be stably atomized during direct printing. This results in films with poor continuity, poor performance, and low quality, ultimately hindering large-scale applications. Therefore, controlling the properties of the precursor solution to ensure stable atomization and promote the self-assembly of graphene oxide nanosheets is crucial for preparing large-area, high-performance reduced graphene oxide films. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a method for preparing reduced graphene oxide films based on electrofluid atomization printing, which can obtain large-area, high-performance reduced graphene oxide films. This invention uses a specific graphene oxide precursor solution, ensuring it meets the conditions for electrofluid atomization printing and promoting the self-assembly of graphene oxide nanosheets. The high-performance graphene oxide film is prepared on a substrate by atomizing the graphene oxide precursor solution using an electrofluidic device, and then reduced to a high-performance reduced graphene oxide film using a chemical reduction method. This invention utilizes commercially available graphene oxide suspensions and other materials to prepare the graphene oxide precursor solution for stable atomization printing using an electrofluidic device to prepare large-area, high-performance reduced graphene oxide films. The prepared graphene oxide films have uniform thickness, strong continuity, and superior performance after reduction, making them suitable for large-scale applications. Furthermore, this method is simple and flexible, significantly reducing the production cost of reduced graphene oxide films and making it suitable for large-scale industrial production.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] This invention provides a method for preparing reduced graphene oxide films based on electrohydrodynamic atomization printing, comprising the following steps:

[0011] (1) A graphene oxide liquid film was obtained on the substrate surface by electrohydrodynamic atomization inkjet printing of the graphene oxide precursor solution.

[0012] (2) The graphene oxide liquid film is dried to obtain a graphene oxide dry film.

[0013] (3) Reduced graphene oxide film is obtained by chemical reduction of dry graphene oxide film;

[0014] The graphene oxide precursor solution is a mixed solution of graphene oxide suspension and organic solvent; the graphene oxide suspension is a deionized aqueous suspension.

[0015] In a preferred embodiment, in step (1), the graphene oxide suspension is an aqueous suspension of graphene oxide nanosheets;

[0016] Preferably, the aqueous suspension of graphene oxide nanosheets is prepared by a modified Hofmann method or a modified Hummers method;

[0017] Preferably, the graphene oxide nanosheet suspension prepared by the modified Hofmann method or the modified Hummers method is a graphene oxide nanosheet suspension with low carboxyl groups; the monolayer ratio of the graphene oxide nanosheets is ≥99.5%, the carboxyl content is 20-30%, and the average radial size is 5-50 μm; in the technical solution of the present invention, the graphene oxide nanosheets with low carboxyl groups can weaken the interaction with water and the nanosheets, which facilitates their good suspension in the liquid phase, facilitates electro-spraying atomization, and promotes stable atomization. In addition, the graphene oxide nanosheets with low carboxyl groups are easy to self-assemble on the substrate, avoid their gelation, and can control the continuity and thickness uniformity of the film. More importantly, the graphene oxide nanosheets with low carboxyl groups are easy to subsequently reduce, which facilitates the preparation of high-quality reduced graphene oxide films; excessively high carboxyl content is not conducive to the self-assembly of graphene oxide nanosheets on the substrate, resulting in uneven graphene oxide films, easy formation of wrinkles, and large surface roughness of the film. Meanwhile, a high carboxyl content requires a long reduction time, which will reduce the performance of the subsequent reduced graphene oxide film.

[0018] In some specific embodiments, the graphene oxide suspension can be a commercially available graphene oxide suspension (e.g., from GOXI Technology, CarbonFeng Technology, and Jicang Nano).

[0019] In a preferred embodiment, in step (1), the graphene oxide precursor solution is a mixed solution of 1-10 mg / mL graphene oxide nanosheet aqueous suspension and organic solvent in a volume ratio of 2-4:6-8.

[0020] Preferably, the organic solvent is selected from at least one of ethanol, acetone, dimethylformamide (DMF), ethylene glycol, isopropanol, propylene carbonate (PC), dimethyl sulfoxide (DMSO), and ethyl acetate. In the technical solution of the present invention, the organic solvent is used to regulate the properties of the precursor solution, thereby reducing the surface tension and increasing the boiling point of the precursor solution, ensuring that the precursor solution can be stably atomized, and preventing the droplets from drying during the process of falling onto the substrate, which would cause the graphene oxide nanosheets to shrink, thus promoting the self-assembly of the graphene oxide nanosheets on the substrate.

[0021] Preferably, the preparation method of the graphene oxide precursor solution includes the following steps: mixing the aqueous suspension of graphene oxide nanosheets with an organic solvent, followed by sonication for 1-3 hours, oscillation for 10-30 minutes, and then vacuum treatment for 10-30 minutes; in the technical solution of the present invention, the graphene oxide nanosheets in the graphene oxide precursor solution obtained by the above preparation method are uniformly dispersed, and the solution is free of agglomeration and bubbles.

[0022] In some specific implementations, in step (1), the electrofluid atomization inkjet printing method uses an integrated, high-precision electro-inkjet printing device;

[0023] Preferably, in the electrohydrodynamic atomization printing method, the nozzle diameter is 250–500 μm, the printing flow rate is 1.4–2 μL / min, and the printing height is 3–7 mm; the nozzle feed spacing is 0.1–0.5 mm, which is the distance the nozzle moves each time along the path; the printing speed is 3–8 mm / s; the nozzle is a single nozzle or an array of nozzles; the voltage applied to the nozzle is +3 kV to +5 kV, and the voltage applied to the substrate is negative, with an application range of -0.5 kV to -2 kV; in the technical solution of the present invention, the negative voltage applied to the substrate can ensure the atomization stability of the graphene oxide precursor solution and improve the self-assembly effect of graphene oxide nanosheets on the substrate; in some specific embodiments, printing can be repeated once or multiple times according to the film thickness requirements.

[0024] In the technical solution of this invention, the material of the substrate is not particularly limited, as long as it is flat. In some specific embodiments, the material of the substrate is selected from polymer materials, metal materials, or ceramic materials; the polymer materials may specifically include polyethylene terephthalate (PET), polyimide (PI), polydimethylsiloxane (PDMS), polytetrafluoroethylene, paper, fabric, etc.; the metal materials may specifically include copper, aluminum, iron, cobalt, nickel, zinc, magnesium, etc., and their alloys; the ceramic materials may specifically include alumina, zirconium oxide, titanium oxide, and silicon oxide, etc.

[0025] As a preferred embodiment, in step (2), the drying is performed at 50-80°C for 0.5-2 hours; in the technical solution of the present invention, low-temperature drying (50-80°C) can prevent the graphene oxide film from shrinking during the drying process, and ensure that a high-performance graphene oxide dry film with low surface roughness is obtained.

[0026] Preferably, the thickness of the graphene oxide dry film is 0.8 nm to 10 μm, and the surface roughness is 0.1 to 3 nm.

[0027] In a preferred embodiment, step (3) of the chemical reduction method includes the following steps:

[0028] The graphene oxide dry film was vaporized by constant temperature heating in a closed space containing a mixed solution of hydroiodic acid and glacial acetic acid. Then, the iodine generated by the reduction and the residual glacial acetic acid were removed by heating.

[0029] Alternatively, the graphene oxide dry film can be chemically reduced by immersing it in a mixed solution of hydroiodic acid and glacial acetic acid, and then the iodine generated during reduction and the residual glacial acetic acid can be removed by heating.

[0030] Preferably, the hydroiodic acid-glacial acetic acid mixed solution is a mixed solution in which the volume ratio of hydroiodic acid to glacial acetic acid is 1:1 to 3;

[0031] Preferably, the constant temperature heating temperature is 95℃~100℃, and the constant temperature heating time is 8~10 hours;

[0032] Preferably, the soaking temperature is 20–30°C, and the soaking time is 5–8 hours;

[0033] Preferably, the process of removing the reduced iodine and residual glacial acetic acid by heating involves heating at 100–150°C for 10–12 hours.

[0034] In the technical solution of this invention, the thickness of the reduced graphene oxide film is 0.5 nm to 10 μm, the surface roughness is 0.1 to 2 nm, the sheet resistance is ≤1.6 kΩ / sq, and the electron mobility is ≥700 cm⁻¹. 2 V -1 s -1 .

[0035] The above technical solution has the following advantages or beneficial effects:

[0036] This invention obtains a high-performance reduced graphene oxide film by controlling the properties of the graphene oxide precursor solution to meet the conditions for electrofluid atomization printing and promoting the self-assembly of graphene oxide nanosheets.

[0037] Compared with the prior art, the present invention has the following advantages:

[0038] (1) The present invention uses a method of electro-printing atomization of low carboxyl group graphene oxide nanosheets, which solves the problem that graphene oxide suspension cannot be stably atomized in the electro-printing process in the prior art, and thus realizes the preparation of large area high quality reduced graphene oxide by electro-printing equipment.

[0039] (2) By controlling the properties of the graphene oxide precursor solution and the potential difference between the nozzle and the substrate, the present invention ensures the stable atomization of the precursor solution and obtains a high-quality reduced graphene oxide film with good self-assembly effect, good continuity, small thickness (less than 50 nm), small surface roughness and high electron mobility.

[0040] (3) The process of this invention is simple and low in cost, which solves the problem that existing technologies are difficult to scale up and apply. Moreover, the manufacturing equipment is easy to integrate and can be used to achieve efficient "roll-to-roll" continuous preparation of large-area, high-quality reduced graphene oxide films. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the process of preparing graphene oxide liquid film using electrohydrodynamic atomization inkjet printing equipment in Embodiment 1 of the present invention.

[0042] Figure 2 This is a stable atomization diagram of the precursor solution being printed using an electrohydrodynamic atomization printing device in Embodiment 1 of the present invention.

[0043] Figure 3 This is a process flow diagram of the preparation of reduced graphene oxide film based on electrofluid atomization inkjet printing method in Embodiment 1 of the present invention.

[0044] Figure 4 This is a scanning electron microscope image of the reduced graphene oxide film prepared in Example 1 of this invention.

[0045] Figure 5 This is an atomic force microscope image (characterizing thickness) of the reduced graphene oxide film prepared in Example 1 of this invention.

[0046] Figure 6 This is an atomic force microscope image (characterizing surface roughness) of the reduced graphene oxide film prepared in Example 1 of the present invention.

[0047] Figure 7 This is a sheet resistance characterization diagram of the reduced graphene oxide film prepared in Example 1 of the present invention. Detailed Implementation

[0048] The following embodiments are merely some, not all, of the embodiments of the present invention. Therefore, the detailed descriptions of the embodiments provided below are not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0049] In this invention, unless otherwise specified, all equipment and raw materials are commercially available or commonly used in the industry. The methods described in the following embodiments are conventional methods in the art, unless otherwise specified.

[0050] Example 1:

[0051] like Figure 3 As shown, the preparation of reduced graphene oxide film based on electrohydrodynamic atomization printing in this embodiment includes the following steps:

[0052] (1) A modified Hofmann method was used to prepare low-carboxylated graphene oxide nanosheets. The specific preparation steps were as follows: 175 mL of 80% concentrated sulfuric acid was added to a round-bottom flask, and 100 mL of 75% concentrated nitric acid was slowly added and stirred continuously in an ice-water bath. After the mixed solution was cooled, 10 g of flake graphite powder was added and evenly dispersed. 110 g of KClO3 was added very slowly. After the KClO3 was completely dissolved, the ice bath was removed, and the reaction was allowed to proceed at room temperature for 96 hours. Finally, the oxidation process was terminated by diluting the obtained slurry dispersion with 1000 mL of deionized water. The graphene oxide solution was centrifuged at 3000 rpm using a rotary centrifuge to separate the upper layer solution and obtain an aqueous suspension of graphene oxide nanosheets. In this example, the concentration of the aqueous suspension of graphene oxide nanosheets was 5 mg / mL, the monolayer ratio of graphene oxide nanosheets was >99.5%, the carboxyl content was 25%, and the average radial size was 25 μm.

[0053] (2) Take 3 mL of the above-mentioned aqueous suspension of graphene oxide nanosheets, 3 mL of propylene carbonate (PC, analytical grade >99.7%), and 4 mL of anhydrous ethanol (analytical grade >99.5%) and add them to a 15 mL glass bottle in sequence. Place the glass bottle in an ultrasonic cleaner and sonicate for 2 hours. Then place it in an oscillator and oscillate for 20 minutes. Finally, place it in a vacuum chamber and evacuate for 20 minutes to obtain the graphene oxide precursor solution.

[0054] (3) The electrofluid atomization inkjet printing process in this embodiment is as follows: Figure 1As shown, a 1mL syringe is used to draw 0.5mL of graphene oxide precursor solution. The syringe with the metal needle is fixed to the flow pump of the inkjet printer as the printhead, with the metal needle serving as the nozzle. Its diameter is 250μm. The flow rate of the flow pump is set to 1.4μL / min. A 1mm thick, 4-inch diameter silicon dioxide wafer is used as the substrate and placed on the XY-axis moving platform. The distance between the needle and the substrate is controlled to be 5mm, the needle movement interval to be 0.2mm, and the translation speed (i.e., printing speed) of the XY-axis moving platform to be 5mm / s. The needle is moved to a non-working area, the metal needle is connected to a positive high voltage of 3kV, and the substrate is connected to a negative high voltage of -1kV. The flow pump is turned on. Figure 2 As shown, after confirming that the solution atomization in the nozzle area is stable, the printing program is started and printing is performed step by step. After printing once on the substrate surface, a graphene oxide liquid film (GO liquid film) is obtained.

[0055] (4) The printed graphene oxide liquid film was transferred to a heating stage with a fume hood. The heating stage temperature was set to 70°C and heated for 30 minutes. After the solvent was completely evaporated, a graphene oxide dry film (GO dry film) was obtained with a thickness of 0.8 nm and a surface roughness of 0.2 nm.

[0056] (5) The graphene oxide dry film obtained in step (4) and the hydroiodic acid-glacial acetic acid (volume ratio = 1:1) mixed solution are placed together in a sealed glass chamber (the dry film is not immersed in the mixed solution). The sealed glass chamber is placed in an oil bath and heated at a constant temperature for steam reduction. The oil bath temperature is set to 95°C and heated for 8 hours. The reduced graphene oxide film after the reaction is taken out and placed on a heating table with a fume hood and heated at 100°C for 12 hours. After removing the reduced iodine and residual glacial acetic acid, a high-quality reduced graphene oxide film (rGO film) is obtained.

[0057] The scanning electron microscope image of the reduced graphene oxide film prepared in this embodiment is shown below. Figure 4 As shown; from Figure 5 and Figure 6 As can be seen from the data, the thickness of the reduced graphene oxide film prepared in this embodiment is 0.5 nm, and the surface roughness Ra is 0.1 nm; from... Figure 7 As can be seen from the data, the average sheet resistance of the reduced graphene oxide film prepared in this embodiment is 1.35 kΩ / sq, and the calculated electron mobility is 800 cm⁻¹. 2 V -1 s -1 .

[0058] Example 2:

[0059] like Figure 3 As shown, the preparation of reduced graphene oxide film based on electrohydrodynamic atomization printing in this embodiment includes the following steps:

[0060] (1) A modified Hummers method was used to prepare low-carboxylated graphene oxide nanosheets. The specific preparation steps were as follows: 90 mL of 80% concentrated sulfuric acid was added to a round-bottom flask, and 50 mL of 75% concentrated nitric acid was slowly added under ice-water bath stirring conditions. After the mixed solution was cooled, 5 g of flake graphite powder was added and evenly dispersed. 9 g of potassium permanganate powder was added in batches over 30 minutes until completely dissolved. The ice-water bath was removed, and the oxidation reaction was started and continued for 8 hours. Finally, the obtained slurry dispersion was diluted with 1000 mL of deionized water to terminate the oxidation process. The graphene oxide solution was centrifuged at 3000 rpm using a rotary centrifuge to separate the upper layer solution and obtain an aqueous suspension of graphene oxide nanosheets. The concentration of the graphene oxide nanosheet suspension prepared in this example was 6 mg / mL, the monolayer rate of the graphene oxide nanosheets was >99.5%, the carboxyl content was 30%, and the average radial size was 30 μm.

[0061] (2) Take 2 mL of the above-mentioned aqueous suspension of graphene oxide nanosheets, 4 mL of propylene carbonate (PC, analytical grade >99.7%), and 4 mL of anhydrous ethanol (analytical grade >99.5%) and add them to a 15 mL glass bottle in sequence. Place the glass bottle in an ultrasonic cleaner and sonicate for 2 hours, then place it in an oscillator and oscillate for 20 minutes. Finally, place it in a vacuum chamber and evacuate for 20 minutes to obtain the graphene oxide precursor solution.

[0062] (3) The electrofluid atomization inkjet printing process in this embodiment is as follows: Figure 1 As shown, a 1mL syringe is used to draw 0.5mL of graphene oxide precursor solution. The syringe with the metal needle is fixed to the flow pump of the inkjet printer as the printhead, with the metal needle serving as the nozzle. Its diameter is 250μm. The flow rate of the flow pump is set to 1.4μL / min. A 1mm thick, 4-inch diameter silicon dioxide wafer is used as the substrate and placed on the XY-axis moving platform. The distance between the needle and the substrate is controlled to be 5mm, the needle movement interval to be 0.2mm, and the translation speed (i.e., printing speed) of the XY-axis moving platform to be 5mm / s. The needle is moved to a non-working area, the metal needle is connected to a positive high voltage of 3.2kV, and the substrate is connected to a negative high voltage of -0.9kV. The flow pump is turned on. Figure 2 As shown, after confirming that the solution atomization in the nozzle area is stable, the printing program is started and printing is performed step by step. After printing once on the substrate surface, a graphene oxide liquid film (GO liquid film) is obtained.

[0063] (4) The printed graphene oxide liquid film was transferred to a heating stage with a fume hood. The heating stage temperature was set to 70°C and heated for 30 minutes. After the solvent was completely evaporated, a graphene oxide dry film (GO dry film) was obtained with a thickness of 2nm and a surface roughness of 0.5nm.

[0064] (5) The graphene oxide dry film obtained in step (4) and the hydroiodic acid-glacial acetic acid (volume ratio = 1:1.5) mixed solution are placed together in a sealed glass chamber (the dry film is not immersed in the mixed solution). The sealed glass chamber is placed in an oil bath and heated at a constant temperature for steam reduction. The oil bath temperature is set to 95°C and heated for 8 hours. The reduced graphene oxide film after the reaction is taken out and placed on a heating table with a fume hood and heated at 100°C for 12 hours. After removing the reduced iodine and residual glacial acetic acid, a high-quality reduced graphene oxide film (rGO film) is obtained.

[0065] The reduced graphene oxide film prepared in this embodiment has a thickness of 1.5 nm, a surface roughness Ra of 0.32 nm, an average sheet resistance of 1.5 kΩ / sq, and a calculated electron mobility of 700 cm⁻¹. 2 V -1 s -1 .

[0066] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing reduced graphene oxide films based on electrohydrodynamic atomization printing, characterized in that, Includes the following steps: (1) A graphene oxide liquid film was obtained on the substrate surface by electrohydrodynamic atomization inkjet printing method using a graphene oxide precursor solution. (2) The graphene oxide liquid film is dried to obtain a graphene oxide dry film; (3) Reduced graphene oxide film is obtained by chemical reduction of dry graphene oxide film; In step (1), in the electrohydrodynamic atomization printing method, the diameter of the nozzle is 250~500 μm, the printing flow rate is 1.4~2 μL / min, and the printing height is 3~7 mm; the feed spacing of the nozzle is 0.1~0.5 mm, which is the distance the nozzle moves each time it moves along the path; the printing speed is 3~8 mm / s; the nozzle is a single nozzle or an array of nozzles; the voltage applied to the nozzle is +3kV~+5kV, and the voltage applied to the substrate is negative, with an application range of -0.5 kV~-2kV; the graphene oxide precursor solution is a mixed solution of graphene oxide suspension and organic solvent; the graphene oxide suspension is a deionized aqueous suspension.

2. The method according to claim 1, characterized in that, In step (1), the graphene oxide suspension is an aqueous suspension of graphene oxide nanosheets.

3. The method according to claim 2, characterized in that, The aqueous suspension of graphene oxide nanosheets was prepared by a modified Hofmann method or a modified Hummers method.

4. The method according to claim 3, characterized in that, The graphene oxide nanosheet suspension prepared by the modified Hofmann method or the modified Hummers method is a graphene oxide nanosheet suspension with low carboxyl groups; the monolayer ratio of the graphene oxide nanosheets is ≥99.5%, the carboxyl content is 20~30%, and the average radial size is 5~50 μm.

5. The method according to claim 2, characterized in that, In step (1), the graphene oxide precursor solution is a mixed solution of 1~10 mg / mL graphene oxide nanosheet aqueous suspension and organic solvent in a volume ratio of 2~4:6~8.

6. The method according to claim 5, characterized in that, The organic solvent is selected from at least one of ethanol, acetone, dimethylformamide (DMF), ethylene glycol, isopropanol, propylene carbonate (PC), dimethyl sulfoxide (DMSO), and ethyl acetate.

7. The method according to claim 2, characterized in that, In step (1), the preparation method of the graphene oxide precursor solution includes the following steps: mixing the aqueous suspension of graphene oxide nanosheets with an organic solvent, sonicating for 1-3 hours, oscillating for 10-30 minutes, and then vacuuming for 10-30 minutes.

8. The method according to claim 1, characterized in that, In step (2), the drying process is carried out at 50~80℃ for 0.5~2 hours.

9. The method according to claim 1, characterized in that, In step (2), the thickness of the graphene oxide dry film is 0.8 nm to 10 μm and the surface roughness is 0.1 to 3 nm.

10. The method according to claim 1, characterized in that, In step (3), the chemical reduction method includes the following steps: The graphene oxide dry film is vaporized by heating at a constant temperature in a sealed space containing a mixture of hydroiodic acid and glacial acetic acid, and then the generated iodine and residual glacial acetic acid are removed by heating; or, the graphene oxide dry film is chemically reduced by immersing it in a mixture of hydroiodic acid and glacial acetic acid, and then the generated iodine and residual glacial acetic acid are removed by heating.

11. The method according to claim 10, characterized in that, In step (3), the hydroiodic acid-glacial acetic acid mixed solution is a mixed solution in which the volume ratio of hydroiodic acid and glacial acetic acid is 1:1~3.

12. The method according to claim 10, characterized in that, In step (3), the temperature of the constant temperature heating is 95℃~100℃, and the time of the constant temperature heating is 8~10 hours.

13. The method according to claim 10, characterized in that, In step (3), the soaking temperature is 20~30℃ and the soaking time is 5~8 hours.

14. The method according to claim 10, characterized in that, The process of removing the reduced iodine and residual glacial acetic acid by heating involves heating at 100-150°C for 10-12 hours.

15. The method according to claim 1, characterized in that, The reduced graphene oxide film has a thickness of 0.5 nm to 10 μm, a surface roughness of 0.1 to 2 nm, a sheet resistance ≤ 1.6 kΩ / sq, and an electron mobility ≥ 700 cm⁻¹. 2 V -1 s -1 .

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