Method for preparing reduced graphene oxide film based on electrofluid atomization spray printing

Abstract

The invention discloses a method for preparing a reduced graphene oxide film based on electrofluid atomization spray printing. The method comprises the following steps: (1) preparing a graphene oxide liquid film from a graphene oxide precursor solution on the surface of a substrate through an electrofluid atomization spray printing method; (2) drying the graphene oxide liquid film to obtain a graphene oxide dry film; (3) performing chemical reduction on the graphene oxide dry film to obtain a reduced graphene oxide film; wherein the graphene oxide precursor solution is a mixed solution of a graphene oxide suspension and an organic solvent; the graphene oxide suspension is deionized water phase suspension. The specific graphene oxide precursor solution is adopted, so that the specific graphene oxide precursor solution meets the electrofluid atomization spray printing condition, self-assembly of graphene oxide nanosheets is promoted, and finally large-scale preparation of the high-performance reduced graphene oxide film is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of two-dimensional material film preparation, and in particular to a method for preparing a reduced graphene oxide film based on electrofluid atomization printing. Background Art

[0002] In recent years, two-dimensional (2D) van der Waals (vdW) layered materials, including graphene, transition metal dihydrides (TMDs), hexagonal boron nitride (h-BN), and MXenes, have attracted widespread attention due to their unique physicochemical properties. Typically, the lateral size of vdW materials can only reach tens of micrometers, which limits their application. Therefore, it is urgent to develop a process method that can synthesize high-performance 2D vdW materials on a large scale.

[0003] Graphene has broad application prospects and can be used in electronics, defense, health care, energy and other fields. However, it has not been commercialized in the true sense. At present, commercial graphene films on the market are all prepared by chemical vapor deposition (CVD). The CVD method for preparing graphene films is complex, requires a high temperature and high pressure environment, is costly, and difficult to transfer.

[0004] Graphene oxide (GO) nanosheets have been shown to be universal two-dimensional building blocks for various macrostructures (such as films or fibers). The performance of high-quality single-layer GO films after reduction can be close to that of graphene films prepared by CVD. However, in order to give full play to the performance of GO, it is crucial to prepare high-quality reduced GO films and ensure the alignment and directional arrangement of GO nanosheets. Traditional methods for preparing GO films, such as vacuum filtration (VF), interfacial assembly, Langmuir-BLodgett assembly, and gel-film conversion (GFT), are difficult to control the assembly process of GO nanosheets, and the thickness of the prepared films is difficult to reach the nanometer level. In addition, the prepared films have poor performance and low quality, which limits their large-scale application.

[0005] As an emerging micro-nano processing technology, electrofluidic printing can be used to produce functional materials with micro-nano characteristic structures. The principle of electrofluidic printing is to eject the precursor solution from the top of the Taylor cone in a "pulling" manner under the drive of the spatial electric field into droplets with extremely small diameters. It has three modes: electrofluidic dot spraying, electrofluidic spinning and electrofluidic atomization. Different printing modes can be achieved according to the properties of the precursor solution. Among them, electrofluidic atomization printing has the characteristics of tiny droplets (nanoscale), large area and uniformity, which is suitable for the preparation of micro-nano thin film materials.

[0006] The most important thing in preparing high-performance two-dimensional material films using two-dimensional nanomaterials is to control the thickness and surface roughness of the film. In the prior art, for example, Wuhan Huaweike Intelligent Technology Co., Ltd.'s SN201807129 electrospray printing device discloses that it can be used for graphene, but the film thickness prepared by the disclosed device exceeds 50nm, and the surface roughness of the prepared graphene film is large, resulting in poor performance.

[0007] In principle, electrofluidic atomization printing can be used to prepare large-area high-quality two-dimensional material films, but it has certain difficulties in actual operation. The applicant previously found that the key to preparing high-quality thin film materials using electrofluidic printing methods is the precursor solution. For graphene materials, the use of electrofluidic printing equipment to prepare thin films requires the preparation of its two-dimensional nanomaterials as liquid suspensions, and the graphene suspension solution prepared by the existing method is easy to precipitate or its graphene oxide suspension cannot be directly used for electrofluidic atomization printing film making, or the suspension cannot be stably atomized when directly printed, resulting in poor continuity, poor performance, low quality of the prepared film, and thus cannot be used for large-scale applications. Therefore, it is essential to regulate the properties of the precursor solution to ensure its stable atomization and promote the self-assembly of graphene oxide nanosheets for the preparation of large-area high-performance reduced graphene oxide films. Summary of the invention

[0008] In view of the above technical problems, the present invention provides a method for preparing a reduced graphene oxide film based on electrofluidic atomization printing, and the method can obtain a large-area, high-performance reduced graphene oxide film. The present invention adopts a specific graphene oxide precursor solution to satisfy the conditions of electrofluidic atomization printing and promote the self-assembly of graphene oxide nanosheets, and prepares a high-performance graphene oxide film on a substrate by atomizing and printing the graphene oxide precursor solution through an electrofluidic device, and reduces it by a chemical reduction method to obtain a high-performance reduced graphene oxide film. The present invention adopts a commercialized graphene oxide suspension in the prior art, etc., and is used for the stable atomization spraying of an electrofluidic device to prepare a large-area high-performance reduced graphene oxide film, and the prepared graphene oxide film has a uniform thickness, strong continuity, and the performance of the graphene film after reduction is superior, and can be applied on a large scale. And the method is simple and flexible, can greatly reduce the production cost of the reduced graphene oxide film, and is suitable for large-scale industrial production.

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

[0010] The present invention provides a method for preparing a reduced graphene oxide film based on electrofluidic atomization printing, comprising the following steps:

[0011] (1) obtaining a graphene oxide liquid film on a substrate surface by electrofluidic atomization printing of a graphene oxide precursor solution;

[0012] (2) drying the graphene oxide liquid film to obtain a graphene oxide dry film;

[0013] (3) chemically reducing the graphene oxide dry film to obtain a reduced graphene oxide film;

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

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

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

[0017] Preferably, the graphene oxide nanosheet suspension prepared by the improved Hofmann method or the improved Hummers method is a graphene oxide nanosheet suspension with few carboxyl groups; the monolayer rate of the graphene oxide nanosheet is ≥99.5%, the carboxyl content is 20-30%, and the average radial size is 5-50 μm; in the technical scheme of the present invention, the graphene oxide nanosheet with few carboxyl groups can weaken the interaction with water and the nanosheets, so that it is convenient for it to maintain a good suspension state in the liquid phase, convenient for electrospray atomization, and can promote its stable atomization. In addition, the graphene oxide nanosheet with few carboxyl groups is convenient for self-assembly on the substrate, avoiding its gelation, and can regulate the continuity and thickness uniformity of the film. More importantly, the graphene oxide nanosheet with few carboxyl groups is easy to be subsequently reduced, so as to prepare high-quality reduced graphene oxide films; too high a carboxyl content is not conducive to the self-assembly of the graphene oxide nanosheets on the substrate, resulting in uneven prepared graphene oxide films, easy formation of wrinkles, and large roughness of the film surface. At the same time, a high carboxyl content requires a long reduction time, which will reduce the performance of the subsequent reduced graphene oxide film;

[0018] In certain specific embodiments, the graphene oxide suspension can directly adopt commercial graphene oxide suspension (such as Gaoxun Technology, Carbonfeng Technology, and Jicang Nano).

[0019] As 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 an 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, so that the surface tension of the precursor solution is reduced and the boiling point is increased, so as to ensure that the precursor solution can be stably atomized, and at the same time, the droplets are prevented from drying in the process of falling to the substrate, resulting in the shrinkage of the graphene oxide nanosheets, and promoting the self-assembly of the graphene oxide nanosheets on the substrate;

[0021] Preferably, the method for preparing the graphene oxide precursor solution comprises the following steps: mixing an aqueous suspension of graphene oxide nanosheets with an organic solvent, ultrasonicating for 1 to 3 hours, oscillating for 10 to 30 minutes, and then vacuuming for 10 to 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 has no agglomeration and bubbles.

[0022] In certain specific embodiments, in step (1), the electrofluidic atomization printing method uses an integrated, high-precision electrospray printing device;

[0023] Preferably, in the electrofluid atomization printing method, the diameter of the nozzle 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, and the feed spacing of the nozzle is the distance the nozzle moves each time when it moves along the path; the printing speed is 3-8 mm / s; the nozzle is a single nozzle or an array nozzle; the voltage applied to the nozzle is +3kV-+5kV, and the voltage connected to the substrate is negatively charged, and the application range is -0.5kV--2kV; in the technical solution of the present invention, the substrate is negatively charged to ensure the atomization stability of the graphene oxide precursor solution, and at the same time improve the self-assembly effect of the 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 the present 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 can specifically include polyethylene terephthalate (PET), polyimide (PI), polydimethylsiloxane (PDMS), polytetrafluoroethylene, paper base, cloth, etc.; the metal materials can specifically include copper, aluminum, iron, cobalt, nickel, zinc, magnesium, etc. and their alloy materials; the ceramic materials can specifically include aluminum oxide, 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 shrinkage of the graphene oxide film during the drying process, thereby ensuring that a high-performance graphene oxide dry film with low surface roughness is obtained;

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

[0027] As a preferred embodiment, in step (3), the chemical reduction method comprises the following steps:

[0028] The graphene oxide dry film is placed in a closed space with a mixed solution of hydroiodic acid and glacial acetic acid by constant temperature heating for steam reduction, and then the iodine element generated by the reduction and the residual glacial acetic acid are removed by heating;

[0029] Alternatively, the graphene oxide dry film is immersed in a mixed solution of hydroiodic acid and glacial acetic acid for chemical reduction, and then the iodine element generated by the reduction and the residual glacial acetic acid are 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°C to 100°C, and the constant temperature heating time is 8 to 10 hours;

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

[0033] Preferably, the heating to remove the iodine element generated by reduction and the residual glacial acetic acid is performed by heating at 100 to 150° C. for 10 to 12 hours.

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

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

[0036] The invention obtains a reduced graphene oxide film with high performance by regulating the properties of a graphene oxide precursor solution so that the solution meets the conditions of electrofluid atomization printing and promotes 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 adopts a method for electrospraying atomization of graphene oxide nanosheets with few carboxyl groups, which solves the problem that the graphene oxide suspension in the prior art cannot be stably atomized in the electrospraying process, thereby realizing the preparation of large-area high-quality reduced graphene oxide by electrospraying equipment;

[0039] (2) The present invention ensures stable atomization of the precursor solution by regulating the properties of the graphene oxide precursor solution and the potential difference between the nozzle and the substrate, thereby obtaining 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 the present invention is simple and low in cost, which solves the problem that the existing technology is difficult to mass produce and apply. 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic diagram of the process of preparing a graphene oxide liquid film by an electrofluid atomization printing device in Example 1 of the present invention.

[0042] Figure 2 This is a stable atomization diagram when the precursor solution is printed by the electrofluidic atomization printing device in Example 1 of the present invention.

[0043] Figure 3 It is a process flow chart of preparing reduced graphene oxide film based on electrofluidic atomization printing method in Example 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 the present invention.

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

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

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

[0048] The following embodiments are only some embodiments of the present invention, rather than all embodiments. Therefore, the detailed description in the embodiments of the present invention provided below is not intended to limit the scope of the present invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work belong to the protection scope of the present invention.

[0049] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments are all conventional methods in the art unless otherwise specified.

[0050] Embodiment 1:

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

[0052] (1) A modified Hofmann method is used to prepare a graphene oxide nanosheet with a low carboxyl group, and the specific preparation steps are as follows: 175 mL of 80% concentrated sulfuric acid is added to a round-bottom flask, and 100 mL of 75% concentrated nitric acid is slowly added under stirring in an ice-water bath and continuously stirred and mixed; after the mixed solution is cooled, 10 g of flaky graphite powder is added and evenly dispersed; 110 g of KClO3 is very slowly added, and after the KClO3 is completely dissolved, the ice bath is removed, and the reaction is allowed to proceed at room temperature for 96 hours; finally, the obtained slurry dispersion is diluted with 1000 mL of deionized water to terminate the oxidation process; the graphene oxide solution is centrifuged at a speed of 3000 rpm using a rotary centrifuge, and the upper layer solution is separated to obtain an aqueous suspension of graphene oxide nanosheets; the concentration of the aqueous suspension of graphene oxide nanosheets prepared in this embodiment is 5 mg / mL, the monolayer rate of the graphene oxide nanosheets is>99.5%, the carboxyl content is 25%, and the average radial size is 25 μm;

[0053] (2) 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%) were added to a 15 mL glass bottle in sequence, and the glass bottle was placed in an ultrasonic cleaner for 2 hours, placed in an oscillator for 20 minutes, and finally placed in a vacuum chamber for 20 minutes to obtain a graphene oxide precursor solution;

[0054] (3) The electrofluidic atomization printing process in this embodiment is as follows Figure 1As shown, take a 1mL syringe to extract 0.5mL of graphene oxide precursor solution, fix the syringe with a metal needle on the flow pump of the electrospray printing equipment as a nozzle, and the metal needle is used as a nozzle with a diameter of 250μm; set the flow rate of the flow pump to 1.4μL / min; take a silicon dioxide wafer with a thickness of 1mm and a diameter of 4 inches as a substrate and place it on the XY axis moving platform; control the distance from the needle to the substrate to be 5mm, the needle movement interval to be 0.2mm, the translation speed of the XY axis moving platform (i.e., the printing speed) to be 5mm / s, move the needle to the non-working area, connect the metal needle to the positive high voltage 3kV, and connect the substrate to the negative high voltage -1kV; turn on the flow pump, as shown in FIG. Figure 2 As shown, it is determined that the atomization of the solution 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 moved to a heating table with a fume hood, the heating table 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) placing the graphene oxide dry film obtained in step (4) and a mixed solution of hydroiodic acid-glacial acetic acid (volume ratio = 1:1) in a sealed glass chamber (the dry film is not immersed in the mixed solution), placing the sealed glass chamber in an oil bath and heating it at a constant temperature for steam reduction, the oil bath temperature is set to 95°C, and heating is performed for 8 hours; taking out the reduced graphene oxide film after the reaction, placing it on a heating table in a fume hood and heating it at 100°C for 12 hours, removing the iodine element generated by the reduction and the residual glacial acetic acid, and obtaining a high-quality reduced graphene oxide film (rGO film).

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

[0058] Embodiment 2:

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

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

[0061] (2) 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%) were added to a 15 mL glass bottle in sequence, and the glass bottle was placed in an ultrasonic cleaner for 2 hours, placed in an oscillator for 20 minutes, and finally placed in a vacuum chamber for 20 minutes to obtain a graphene oxide precursor solution;

[0062] (3) The electro-fluid atomization printing process in this embodiment is as follows Figure 1 As shown, take a 1mL syringe to extract 0.5mL of graphene oxide precursor solution, fix the syringe with a metal needle on the flow pump of the electrospray printing equipment as a nozzle, and the metal needle is used as a nozzle with a diameter of 250μm; set the flow rate of the flow pump to 1.4μL / min; take a silicon dioxide wafer with a thickness of 1mm and a diameter of 4 inches as a substrate and place it on the XY axis moving platform; control the distance from the needle to the substrate to be 5mm, the needle movement interval to be 0.2mm, the translation speed of the XY axis moving platform (i.e., the printing speed) to be 5mm / s, move the needle to the non-working area, connect the metal needle to a positive high voltage of 3.2kV, and connect the substrate to a negative high voltage of -0.9kV; turn on the flow pump, as shown in FIG. Figure 2 As shown, it is determined that the atomization of the solution 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 moved to a heating table with a fume hood, the heating table 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 2 nm and a surface roughness of 0.5 nm;

[0064] (5) placing the graphene oxide dry film obtained in step (4) and a mixed solution of hydroiodic acid-glacial acetic acid (volume ratio = 1:1.5) in a sealed glass chamber (the dry film is not immersed in the mixed solution), placing the sealed glass chamber in an oil bath and heating it at a constant temperature for steam reduction, the oil bath temperature is set to 95°C, and heating is performed for 8 hours; taking out the reduced graphene oxide film after the reaction, placing it on a heating table in a fume hood and heating it at 100°C for 12 hours, removing the iodine element generated by the reduction and the residual glacial acetic acid, and obtaining a high-quality reduced graphene oxide film (rGO film).

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

[0066] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing reduced graphene oxide film based on electrofluidic atomization printing, characterized in that: The following steps are involved: (1) obtaining a graphene oxide liquid film on a substrate surface by electrofluidic atomization printing of a graphene oxide precursor solution; (2) drying the graphene oxide liquid film to obtain a graphene oxide dry film; (3) chemically reducing the graphene oxide dry film to obtain a reduced graphene oxide film; The graphene oxide precursor solution is a mixed solution of a graphene oxide suspension and an organic solvent; and the graphene oxide suspension is a deionized water phase 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; Preferably, the graphene oxide nanosheet aqueous suspension is prepared by a modified Hofmann method or a modified Hummers method; Preferably, the graphene oxide nanosheet suspension prepared by the improved Hofmann method or the improved Hummers method is a carboxyl-less graphene oxide nanosheet suspension; the monolayer rate of the graphene oxide nanosheet is ≥99.5%, the carboxyl content is 20-30%, and the average radial size is 5-50 μm.

3. 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 an organic solvent in a volume ratio of 2-4:6-8; 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.

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

5. The method according to claim 1, characterized in that In step (1), in the electrofluid atomization printing method, the diameter of the nozzle 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, and the feed spacing of the nozzle is the distance the nozzle moves each time when it moves along the path; the printing speed is 3-8 mm / s; the nozzle is a single nozzle or an array nozzle; the voltage applied to the nozzle is +3 kV to +5 kV, and the voltage connected to the substrate is negative, and the application range is -0.5 kV to -2 kV.

6. The method according to claim 1, characterized in that In step (2), the drying is performed at 50 to 80° C. for 0.5 to 2 hours; Preferably, the graphene oxide dry film has a thickness of 0.8 nm to 10 μm and a surface roughness of 0.1 to 3 nm.

7. The method according to claim 1, characterized in that In step (3), the chemical reduction method comprises the following steps: The graphene oxide dry film is placed in a closed space with a hydroiodic acid-glacial acetic acid mixed solution and steam-reduced by constant temperature heating, and then the iodine element generated by the reduction and the residual glacial acetic acid are removed by heating; or, the graphene oxide dry film is immersed in a hydroiodic acid-glacial acetic acid mixed solution for chemical reduction, and then the iodine element generated by the reduction and the residual glacial acetic acid are removed by heating; 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 1:1-3.

8. The method according to claim 7, characterized in that The constant temperature heating temperature is 95°C to 100°C, and the constant temperature heating time is 8 to 10 hours; Preferably, the soaking temperature is 20-30° C., and the soaking time is 5-8 hours.

9. The method according to claim 7, characterized in that: The step of removing the iodine element generated by reduction and the residual glacial acetic acid by heating is heating at 100-150° C. for 10-12 hours.

10. 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 square resistance of ≤1.6 kΩ / sq, and an electron mobility of ≥700 cm 2 V -1 s -1 .

Images