Method for forming reduced graphene oxide film, reduced graphene oxide film, and article

Abstract

To provide an efficient method for forming a reduced graphene oxide film using an iodine-based reductant.SOLUTION: A method for forming a reduced graphene oxide film comprises: placing a substrate in a reducing atmosphere containing at least one of iodine and hydrogen iodide; and spraying a dispersion of graphene oxide onto the substrate in the reducing atmosphere to reduce the graphene oxide and simultaneously deposit reduced graphene oxide, which is a reduced product of graphene oxide, on the substrate.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for forming a reduced graphene oxide film, a reduced graphene oxide film, and an article.

Background Art

[0002] Reduced graphene oxide obtained by reducing graphene oxide has attracted attention as a material for transparent electrodes, electromagnetic wave shields, supercapacitors, and the like. In the above applications, it is common to use reduced graphene oxide in the form of a film, and various methods for forming a film containing reduced graphene oxide (hereinafter also referred to as a "reduced graphene oxide film") have been studied. For example, Non-Patent Document 1 discloses a method for forming a reduced graphene oxide film by spraying a mixed solution obtained by mixing graphene oxide and hydrazine onto a pre-heated substrate, thereby simultaneously forming a film and reducing graphene oxide. According to this method, a reduced graphene oxide film can be efficiently formed.

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Although hydrazine is a reducing agent with excellent reduction efficiency, a reducing agent to replace hydrazine has been demanded due to problems such as its toxicity. For example, a method using an iodine-based reducing agent such as hydrogen iodide (HI) instead of hydrazine has been studied. However, as a result of the studies by the present inventors, when an iodine-based reducing agent is used by the method of Non-Patent Document 1, it has been found that the reduction of graphene oxide proceeds rapidly and a problem occurs in that the spray nozzle becomes clogged by the particles of reduced graphene oxide. Therefore, in order to efficiently form a reduced graphene oxide film using an iodine-based reducing agent, a new method alternative to the method of Non-Patent Document 1 has been required.

[0005] Therefore, one of the objects of the present invention is to provide a method for efficiently forming a reduced graphene oxide film using an iodine-based reducing agent.

Means for Solving the Problems

[0006] The present invention provides at least the following [1] to [6].

[0007] [1] Placing a substrate in a reducing atmosphere containing at least one of iodine and hydrogen iodide, and spraying a dispersion of graphene oxide onto the substrate in the reducing atmosphere to reduce the graphene oxide and deposit reduced graphene oxide, which is a reduced form of the graphene oxide, on the substrate, and a method for forming a reduced graphene oxide film including the above.

[0008] [2] The method for forming a reduced graphene oxide film according to [1], wherein the dispersion contains at least one of water and ethanol.

[0009] [3] The method for forming a reduced graphene oxide film according to [1] or [2], wherein the content of graphene oxide in the dispersion is 0.01 to 2 g / L.

[0010] [4] The method for forming a reduced graphene oxide film according to any one of [1] to [3], wherein the reducing atmosphere is formed by heating a solution containing at least one of iodine and hydrogen iodide.

[0011] [5] The transmittance of light with a wavelength of 550 nm is 85 to 99%, The surface resistivity is 1500 to 60000 Ω / sq, A reduced graphene oxide film having a thickness of 0.0005 to 0.1 μm.

[0012] [6] An article comprising a substrate and the reduced graphene oxide film according to [5] provided on the substrate.

Advantages of the Invention

[0013] According to the present invention, an efficient method for forming a reduced graphene oxide film using an iodine-based reducing agent can be provided.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0015] In this specification, a numerical range indicated by using "~" indicates a range including the numerical values described before and after "~" as the minimum value and the maximum value, respectively. Also, unless specifically specified otherwise, the units of the numerical values described before and after "~" are the same. Further, when a plurality of numerical ranges are described stepwise in this specification, the upper limit value or the lower limit value of a numerical range at a certain step may be replaced with the upper limit value or the lower limit value of a numerical range at another step. Also, the upper limit value or the lower limit value of a numerical range may be replaced with the value shown in the examples. Also, the individually described upper limit value and lower limit value can be arbitrarily combined. Also, the materials exemplified below may be used alone or in combination of two or more, unless otherwise specified.

[0016] Hereinafter, preferred embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments at all.

[0017] <Method for Producing Reduced Graphene Oxide Film> One embodiment of the present invention includes disposing a substrate in a reducing atmosphere containing at least one of iodine and hydrogen iodide (hereinafter referred to as "the first step"), and spraying a dispersion of graphene oxide onto the substrate in the above atmosphere to reduce the graphene oxide and deposit reduced graphene oxide, which is a reduced form of graphene oxide, on the substrate (hereinafter referred to as "the second step").

[0018] (The First Step) In the first step, a substrate is disposed in a reducing atmosphere containing at least one of iodine and hydrogen iodide.

[0019] The reducing atmosphere may be a gas atmosphere or an aerosol atmosphere. That is, iodine and hydrogen iodide in the reducing atmosphere may be contained in the reducing atmosphere as a gas or as an aerosol.

[0020] The reducing atmosphere may contain either iodine or hydrogen iodide as a reducing component, or both. The ratio of iodine to hydrogen iodide in the reducing component is not particularly limited, but may be 0:1 to 1:0, 1:3 to 3:1, 1:2 to 1:2, 1:1 to 1:0, or 0:1 to 1:1 by volume ratio.

[0021] The reducing atmosphere may contain a reducing component other than iodine and hydrogen iodide. The total amount of iodine and hydrogen iodide may be 80% by volume or more, 90% by volume or more, or 95% by volume or more based on the total volume of the reducing component.

[0022] The total concentration of iodine and hydrogen iodide in the reducing atmosphere may be appropriately adjusted according to the properties of the desired reduced graphene oxide film. For example, it may be 1 to 20% by volume, 1 to 15% by volume, or 2 to 10% by volume. The higher the total concentration of iodine and hydrogen iodide, the easier the reduction of graphene oxide progresses, and the surface resistivity of the reduced graphene oxide film tends to be lower. In this embodiment, the concentration of iodine in the reducing atmosphere may be within the above range, and the concentration of hydrogen iodide in the reducing atmosphere may be within the above range.

[0023] The substrate has a surface on which the reduced graphene oxide film is formed. The material of the substrate is not particularly limited and may be glass, polyethylene terephthalate (PET), polyimide (PI), metal (such as platinum), etc. Here, examples of the glass include soda lime glass, quartz glass, borosilicate glass, etc. From the viewpoint of easily obtaining a reduced graphene oxide film with high resistance and high transparency, it is preferable that the material of the above surface on which the reduced graphene oxide film is formed has acid resistance (for example, glass, etc.). The substrate may be a porous body. The shape of the substrate is not particularly limited and may be sheet-like, film-like, foil-like, etc.

[0024] In the first step, after forming the reducing atmosphere, the substrate may be placed well in the reducing atmosphere, or the atmosphere of the space where the substrate is placed in advance may be used as the reducing atmosphere.

[0025] The reducing atmosphere may be formed, for example, by heating a solution containing at least one of iodine and hydrogen iodide. Specifically, for example, by heating the plate on which the substrate is placed and dropping a solution containing at least one of iodine and hydrogen iodide onto the plate, iodine and / or hydrogen iodide can be vaporized to form a reducing atmosphere. In this method, by adjusting the heating temperature of the plate, the concentration of the solution, the dropping amount of the solution, etc., the concentration of the reducing components in the atmosphere can be controlled.

[0026] When the solution contains iodine, the heating temperature of the solution may be, for example, 50 to 150 °C, and when the solution contains hydrogen iodide, the heating temperature of the solution may be, for example, 10 to 100 °C. At the above temperatures, the vaporization rate of iodine and hydrogen iodide does not become too fast, so it is easy to control the concentration of iodine and hydrogen iodide in the atmosphere.

[0027] (Second step) In the second step, a dispersion of graphene oxide is sprayed onto the substrate in the reducing atmosphere to reduce the graphene oxide and deposit reduced graphene oxide on the substrate.

[0028] The dispersion of graphene oxide contains graphene oxide and a dispersion medium for dispersing the graphene oxide. Here, "dispersion" refers to a state in which the object (for example, graphene oxide) is suspended or floating, but a part of the object may be in a precipitated state. The method for dispersing graphene oxide is not particularly limited, and graphene oxide may be dispersed by a known method (for example, a method using a ball mill, a bead mill, an ultrasonic homogenizer, etc.).

[0029] Graphene oxide has oxygen-containing functional groups generated by oxidizing graphite. The oxygen-containing functional groups can include at least one functional group selected from the group consisting of, for example, epoxy groups (-COC-), hydroxyl groups (-OH), carbonyl groups (-CO-), and carboxyl groups (-COOH).

[0030] For example, graphene oxide obtained by oxidizing graphite by the Hummers method described in Non-Patent Document 2 can be used. The Hummers method generally includes a step of pretreating graphite by reacting it with a compound selected from ammonium persulfate, phosphorus pentoxide, and sulfuric acid (the first step), and a step of oxidizing the pretreated graphite with sulfuric acid and a strong oxidizing agent (for example, potassium permanganate) (the second step). Usually, the pretreated graphite is washed with water, dried, and then subjected to the second step. The graphite (graphene oxide) oxidized in the second step may be washed with hydrogen peroxide, hydrochloric acid, water, etc. According to this method, powdery graphene oxide can be obtained.

[0031] Examples of the dispersion medium include water, alcohols such as ethanol, and acetone. These may be used alone or in combination of two or more. From the viewpoint of affinity with graphene oxide, it is preferable that the dispersion medium contains at least one of water and ethanol, and more preferably contains water. The dispersion medium may be a mixed solution containing water and ethanol. The ratio of water to ethanol in the dispersion medium is not particularly limited, but may be 0:1 to 1:0, 1:3 to 3:1, 1:2 to 1:2, 1:1 to 1:0, or 0:1 to 1:1 by mass ratio. The total amount of water and ethanol in the dispersion medium may be 80% by mass or more, 90% by mass or more, or 95% by mass or more based on the total mass of the dispersion medium.

[0032] The content of graphene oxide in the dispersion may be 0.01 g / L or more, 0.05 g / L or more, or 0.2 g / L or more from the viewpoints of ensuring a sufficient throughput and enhancing the treatment efficiency. The content of graphene oxide in the dispersion may be 2 g / L or less, 1.5 g / L or less, or 1 g / L or less from the viewpoint of suppressing particle aggregation. From these viewpoints, the content of graphene oxide in the dispersion may be 0.01 to 2 g / L, 0.05 to 1.5 g / L, or 0.2 to 1 g / L.

[0033] Other components other than graphene oxide and the dispersion medium may be blended in the dispersion, but the blending amount of the other components may be 1 g / L or less, 0.1 g / L or less, or 0.01 g / L or less.

[0034] The spraying of the dispersion may be performed using a known sprayer. Examples of the known sprayer include an airbrush (spray gun) and the like. Generally, the sprayer has a spray nozzle, and the dispersion is discharged from the spray nozzle together with the carrier gas under a specific pressure and sprayed into the air as fine droplets (aerosol). At this time, by adjusting the spraying amount of the dispersion, a reduced graphene oxide film with a target film thickness can be obtained. Also, the size of the droplets sprayed can be adjusted by the shape of the spray nozzle, the size of the nozzle diameter, etc. Furthermore, by adjusting the distance from the spray nozzle to the substrate surface, the dispersion time of the droplets and the reduction time of graphene oxide can be sufficiently ensured, and it becomes easier to form a uniform film. The distance from the spray nozzle to the substrate surface can be, for example, 10 to 200 mm.

[0035] Examples of the carrier gas used for spraying the dispersion include carbon dioxide gas, compressed air, nitrogen gas, argon gas, helium gas, hydrogen gas, etc. The supply pressure of the carrier gas can be, for example, 0.2 to 1.0 MPa.

[0036] When spraying the dispersion, the temperatures of the substrate and the atmosphere may be adjusted by known heating means. The temperature of the substrate when spraying the dispersion may be, for example, 10 to 150 °C or 10 to 120 °C, and the temperature of the atmosphere when spraying the dispersion may be, for example, 25 to 100 °C.

[0037] According to the method described above, a reduced graphene oxide film can be formed, and an article comprising a substrate and a reduced graphene oxide film provided on the substrate can be obtained. The article is, for example, a transparent electrode, an electromagnetic wave shield, a supercapacitor, or the like.

[0038] The method of the above embodiment may include a step of treating the reduced graphene oxide film obtained in the second step. For example, the method of the above embodiment may include heat-treating a film composed of the deposit of reduced graphene oxide obtained in the second step. Thereby, the reducing components (iodine or hydrogen iodide) remaining in the film can be removed.

[0039] As a method for forming a reduced graphene oxide film, a method of reducing the graphene oxide film after forming the graphene oxide film or a method of forming a film using a powder of pre-prepared reduced graphene oxide has been common. However, in the method of the above embodiment, since the reduction of graphene oxide and the formation of a film containing reduced graphene oxide (reduced graphene oxide film) generated by the reduction can proceed substantially simultaneously, a reduced graphene oxide film can be formed more efficiently as compared with the above conventional method. Therefore, the method of the above embodiment is suitable for mass production of reduced graphene oxide films.

[0040] In addition, since the graphene oxide film has a property of being easily soluble in water, in the above conventional method of reducing the graphene oxide film, cracking may occur due to the aqueous solution used for reducing the graphene oxide film. However, according to the method of the above embodiment, the occurrence of the above cracking can be prevented.

[0041] In addition, in the method of the above embodiment, heating of the substrate is not essential, and high-temperature annealing or a secondary transfer process is not required. Therefore, it is possible to directly form a film on a substrate made of a material with low heat resistance such as PET.

[0042] Furthermore, according to the method of the above embodiment, it is possible to form a reduced graphene oxide film having high resistance and high transparency. For example, in the method of the above embodiment, it is also possible to form a reduced graphene oxide film having a light transmittance of 85 to 99% at a wavelength of 550 nm, a surface resistivity of 1500 to 60000 Ω / sq, and a thickness of 0.0005 to 0.1 μm. Here, the light transmittance at a wavelength of 550 nm is a value measured using an ultraviolet-visible-infrared spectrophotometer V-550 (manufactured by JASCO Corporation) in accordance with JIS Z8722. The surface resistivity is a value measured using a four-probe resistivity measuring instrument Σ-5+ (manufactured by Nippon Sheet Glass Co., Ltd.) in accordance with JIS K7194 and is also called sheet resistance.

[0043] The light transmittance at a wavelength of 550 nm, the surface resistivity, and the thickness can be adjusted by the concentrations of iodine and hydrogen iodide in a reducing atmosphere, the content of graphene oxide in the dispersion, the spraying amount of the dispersion, etc. The light transmittance at a wavelength of 550 nm can be made more than 0% and 99% or less, or 85 to 95.5%. The surface resistivity can be made 200 to 60000 Ω / sq or 1800 to 56000 Ω / sq, and the thickness can be made 0.0007 to 0.1 μm or 0.0007 to 0.01 μm.

[0044] The reduced graphene oxide film having high resistance and high transparency as described above is suitable as a material for transparent electrodes, electromagnetic shields, etc., and can also be expected to be applied to fields such as flexible and wearable electronics, perovskite solar cells, fuel cells, batteries, supercapacitors, sensors, catalysts, separation membranes, and drug delivery.

[0045] The reduced graphene oxide film obtained by the method of the above embodiment is composed of reduced graphene oxide deposited on a substrate. The reduced graphene oxide includes a partial reduction product of graphene oxide. That is, the reduced graphene oxide has oxygen-containing functional groups. Examples of the oxygen-containing functional groups include an epoxy group (-COC-), a hydroxyl group (-OH), a carbonyl group (-CO-), a carboxyl group (-COOH), and the like. That the reduced graphene oxide has the above functional groups can be confirmed by analysis using XPS (X-ray photoelectron spectroscopy). Note that the reduced graphene oxide film may contain unreduced graphene oxide, but the unreduced graphene oxide is regarded as a part of the reduced graphene oxide.

[0046] The reduced graphene oxide may have bonds attributed to C=C and C=O in the C1s spectrum measured by, for example, XPS. Here, the C1s spectrum refers to a region corresponding to the energy peak position of the 1s orbital of C in the XPS spectrum. The energy peak of the 1s orbital of C is attributed to any bond containing C based on the peak position. The reduced graphene oxide may have bonds attributed to C-O and O-C=O in the C1s spectrum measured by XPS.

[0047] In the C1s spectrum of reduced graphene oxide measured by XPS, the proportion of the bond attributed to C=O is preferably 2% or more, more preferably 4% or more, still more preferably 5% or more, and particularly preferably 6% or more. The proportion of the bond attributed to C=O is preferably 11% or less, more preferably 9% or less, still more preferably 7% or less. From these viewpoints, the proportion of the bond attributed to C=O is preferably 2 to 11%, more preferably 4 to 9%, still more preferably 4 to 7%, even more preferably 5 to 7%, and particularly preferably 6 to 7%. The proportion of the bond attributed to C=O in the C1s spectrum indicates the proportion of the bond attributed to C=O in the total bonds (such as C=O, C-O, and O-C=O) attributed from the peaks observed in the C1s spectrum.

[0048] In the C1s spectrum of reduced graphene oxide measured by XPS, the proportion of the bond attributed to C-O is preferably 0% or more, more preferably 1% or more, still more preferably 2% or more, even more preferably 3% or more, and particularly preferably 4% or more, and most preferably 5% or more. The proportion of the bond attributed to C-O is preferably 15% or less, more preferably 12% or less, still more preferably 10% or less, and particularly preferably 9% or less. From these viewpoints, the proportion of the bond attributed to C-O is preferably 0 to 15%, more preferably 1 to 12%, still more preferably 2 to 12%, even more preferably 3 to 11%, particularly preferably 4 to 11%, and most preferably 5 to 9%. The proportion of the bond attributed to C-O in the C1s spectrum indicates the proportion of the bond attributed to C-O in the total bonds (such as C=O, C-O, and O-C=O) attributed from the peaks observed in the C1s spectrum.

[0049] In the C1s spectrum of reduced graphene oxide measured by XPS, the ratio of the bond assigned to O-C=O is preferably 0% or more, more preferably 0.5% or more, still more preferably 1% or more, even more preferably 1.5% or more, and particularly preferably 2% or more. The ratio of the bond assigned to O-C=O is preferably 5% or less, more preferably 4% or less, still more preferably 3.5% or less. From these viewpoints, the ratio of the bond assigned to O-C=O is preferably 0 to 5%, more preferably 0.5 to 4%, still more preferably 1 to 3.5%, even more preferably 1.5 to 3.5%, and particularly preferably 2 to 3.5%. The ratio of the bond assigned to O-C=O in the C1s spectrum indicates the ratio of the bond assigned to O-C=O in the total bonds (such as C=O, C-O, and O-C=O) assigned from the peaks observed in the C1s spectrum.

[0050] The ratio of the bond assigned to C=O in the C1s spectrum is a value obtained from the peak area ratio of the C1s spectrum, and can also be referred to as the atomic concentration (unit: atm%) of the oxygen atoms constituting the C=O bond. The same applies to the ratios of the bonds assigned to C-O and O-C=O in the C1s spectrum. The XPS can be measured by the method described in the examples.

[0051] Reduced graphene oxide has a bond assigned to C=O in the O1s spectrum measured by XPS. Here, the O1s spectrum refers to the region corresponding to the energy peak position of the 1s orbital of O in the XPS spectrum. The energy peak of the 1s orbital of O is assigned to any bond containing O based on its peak position. Reduced graphene oxide may have a bond assigned to C-O and a bond assigned to C-OH in the O1s spectrum measured by XPS.

[0052] In the O1s spectrum of reduced graphene oxide measured by XPS, the proportion of the bond attributed to C=O is preferably 25% or more, more preferably 30% or more, and still more preferably 60% or more. The proportion of the bond attributed to C=O is preferably 80% or less, more preferably 75% or less, and still more preferably 73% or less. From these viewpoints, the proportion of the bond attributed to C=O may be, for example, 25 to 80%, 25 to 75%, 30 to 75%, or 60 to 73%. The proportion of the bond attributed to C=O in the O1s spectrum indicates the proportion of the bond attributed to C=O in the total bonds (e.g., C=O, C-O, and C-OH) attributed from the peaks observed in the O1s spectrum.

[0053] In the O1s spectrum of reduced graphene oxide measured by XPS, the proportion of the bond attributed to C-O is preferably 0% or more, more preferably 15% or more, still more preferably 20% or more, and particularly preferably 5% or more. The proportion of the bond attributed to C-O is preferably 80% or less, more preferably 70% or less, and still more preferably 30% or less. From these viewpoints, the proportion of the bond attributed to C-O may be, for example, 20 to 30%. The proportion of the bond attributed to C-O in the O1s spectrum indicates the proportion of the bond attributed to C-O in the total bonds (e.g., C=O, C-O, and C-OH) attributed from the peaks observed in the O1s spectrum.

[0054] The proportion of the bond attributed to C=O in the O1s spectrum is a value obtained from the peak area ratio of the O1s spectrum, and can also be referred to as the atomic concentration (unit: atm%) of the oxygen atoms constituting the C=O bond. The same applies to the proportion of the bond attributed to C-O in the O1s spectrum. The XPS can be measured by the method described in the examples.

[0055] The degree of reduction of reduced graphene in the reduced graphene oxide film can be adjusted by the concentrations of iodine and hydrogen iodide in the reducing atmosphere, the distance from the spray nozzle to the substrate surface, and the like.

Example

[0056] Hereinafter, the content of the present invention will be described in more detail using examples and comparative examples. However, the present invention is not limited to the following examples.

[0057] <Preparation Example 1> (Preparation of dispersion of graphene oxide) Graphene oxide (GO) was synthesized from graphite powder (average particle size: 45 μm) by the improved Hummers method. Specifically, first, 60 ml of sulfuric acid (H 2 SO 4 , 95% by mass) was added to a 500 ml beaker and heated to 80 °C. To this, 3.0 g of ammonium persulfate ((NH 4 ) 2 S 2 O 8 , 98% by mass) was added with stirring and dissolved to obtain a solution. Then, 3.0 g of phosphorus pentoxide (P 2 O 5 , 98% by mass) was gradually added to the above solution to obtain a mixture. At this time, it was confirmed that the temperature was maintained at 80 °C. Next, 3.0 g of graphite was added to the obtained mixture, and the mixture was reacted at 80 °C with stirring for 4.5 hours to obtain a graphite mixture. After the reaction, this was kept below 10 °C in an ice bath. Then, 450 ml of DI water (deionized water) was slowly dropped into the above graphite mixture while paying attention to a sudden temperature rise. Then, the ice bath was removed and left standing at room temperature overnight. The mixture after standing was filtered, the filtrate was washed with 2000 ml of DI water, and the washed filtrate was dried at about 45 °C overnight. Thereby, treated graphite was obtained.

[0058] After placing 3.0 g of the obtained treated graphite in a beaker, 150 ml of sulfuric acid was added to the beaker for further oxidation and cooled to near 0 °C in an ice bath. To the cooled solution, 18.0 g of potassium permanganate (KMnO 4 , purity 99.3%) was gradually added while keeping the temperature below 10 °C to obtain a mixed solution. After stirring the obtained mixed solution for 15 minutes, the ice bath was removed and the mixture was stirred and reacted for 2 hours while heating to 35 °C. Next, the stirred mixed solution was cooled again to 0 °C in an ice bath, and 255 ml of DI water was slowly added while paying attention to a sudden temperature rise. Then, the ice bath was removed and the solution was stirred for 2 hours while keeping the temperature of the solution below 35 °C. After completion of stirring, 750 ml of DI water was added to the solution while stirring, and further 5 ml of hydrogen peroxide (H 2 O 2 , 30 mass%) was added and stirred for 2 hours, and then left standing overnight. Thereafter, the supernatant was filtered to obtain a filter paper precipitate and a precipitate at the bottom of the beaker. The obtained filter paper precipitate and beaker precipitate were placed in the same beaker, 250 ml of hydrochloric acid (10 mass%) was added, stirred for 2 hours and then filtered. After repeating the same operation twice, graphene oxide was obtained as the filter paper precipitate and beaker precipitate. 200 mg of the obtained graphene oxide was dissolved in 1000 ml of DI water to obtain an aqueous dispersion of graphene oxide (graphene oxide content: 0.2 mg / ml).

[0059] <Example> (First step) A glass dish (petri dish) was placed on a preheated hot plate (model: HP-19U300, manufactured by KPI (Koike Precision Instruments Co., Ltd.)), and a substrate was placed in the glass dish. Then, after heating the glass dish sufficiently, hydroiodic acid (concentration: about 1.6 g / ml, 55.0 - 58.0 mass%) was dropped onto the bottom of the glass dish to generate hydroiodic acid gas, forming a reducing atmosphere containing hydroiodic acid gas.

[0060] In the above first step, in Examples a1 to a6, the preheating temperature of the hot plate was set to 90°C, and soda lime slide glass (manufactured by Matsunami Glass Industry Co., Ltd., S202356, MICRO SLIDE GLASS) was used for the substrate. The dropping amount of hydrogen iodide was 0.05 ml in Example a1 (a1-1 to a1-7), 0.1 ml in Example a2 (a2-1 to a2-12), 0.2 ml in Example a3 (a3-1 to a3-14), 0.3 ml in Example a4 (a4-1 to a4-9), 0.6 ml in Example a5 (a5-1 to a5-9), and 1.0 ml in Example a6 (a6-1 to a6-8).

[0061] In the above first step, in Examples b1 to b5, soda lime slide glass (manufactured by Matsunami Glass Industry Co., Ltd., S202356, MICRO SLIDE GLASS) was used for the substrate, and the dropping amount of hydrogen iodide was set to 0.2 ml. The preheating temperature of the hot plate was 90°C in Example b1 (b1-1 to b1-14), 100°C in Example b2 (b2-1 to b2-8), 120°C in Example b3 (b3-1 to b3-13), 150°C in Example b4 (b4-1 to b4-10), and 200°C in Example b5 (b5-1 to b5-12). Note that Example b1-1 is the same as Example a3-1.

[0062] In the above first step, in Examples c1 to c4, the preheating temperature of the hot plate was set to 90°C, and the dropping amount of hydrogen iodide was set to 0.2 ml. Soda lime slide glass (manufactured by Matsunami Glass Industry Co., Ltd., S202356, MICRO SLIDE GLASS) was used for the substrate in Example c1 (c1-1 to c1-14), quartz slide glass (manufactured by Matsunami Glass Industry Co., Ltd.) was used in Example c2 (c2-1 to c2-34), polyimide (PI) film (manufactured by Toray DuPont) was used in Example c3 (c3-1 to c3-11), and polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd.) was used in Example c4 (c4-1 to c4-14). Note that Example c1-1 is the same as Example a3-1.

[0063] (Second step) Next, using an airbrush (nozzle diameter 0.5 mm, Mr. Hobby Procon Boy PS-290 trigger airbrush), an aqueous dispersion of graphene oxide prepared in Preparation Example 1 (graphene oxide content: 0.2 mg / ml) was sprayed onto the substrate in the above reducing atmosphere. At this time, the spraying amount was adjusted for each example so that the film thicknesses shown in Tables 1 to 15 were obtained. The gas for spraying (carrier gas) was CO 2 was supplied by a gas cylinder, and the gas supply pressure was 0.4 MPa. Also, the distance from the spray nozzle of the airbrush to the substrate surface was 150 mm.

[0064] By the above operations, reduced graphene oxide films of each example were formed.

[0065] (FT-IR Analysis) Regarding graphene oxide as the material and reduced graphene oxide constituting the reduced graphene oxide of each example, measurement by Fourier transform infrared spectroscopy was performed using FT / IR-6300 (manufactured by JASCO Corporation). On the FT-IR spectrum of graphene oxide, absorption bands of O-H (3408 cm -1 and 1269 cm -1 ), C=O (1720 cm -1 ), C=C (1622 cm -1 ) and C-O (1060 cm -1 ) were confirmed. However, in any of the examples, in the FT-IR spectrum of the reduced graphene oxide, the absorption bands of the oxidized functional groups (C=O, C-O, O-H) were significantly reduced, and in particular, it was confirmed that the absorption band of O-H near 3408 cm -1 had disappeared. For reference, the FT-IR spectra of graphene oxide (GO) and reduced graphene oxide (rGO) of Example a3-8 are shown in FIG. 1.

[0066] (XPS Analysis) X-ray photoelectron spectroscopy (XPS) analysis was performed on graphene oxide as the material and the reduced graphene oxide constituting the reduced graphene oxide film of each example using an ESCA3400 spectrometer manufactured by Shimadzu Corporation. MgKα (hv = 1.2536 keV) was used as the X-ray source. As a result of the XPS analysis, in the reduced graphene oxide of the examples, the binding energy peak between carbon and oxygen was much lower than the binding energy peak between carbon and oxygen in graphene oxide, and it was confirmed that the oxygen functional groups were significantly reduced. Also, the C / O ratio was 2.3 for graphene oxide, but about 12 for the reduced graphene oxide of the examples. From this, too, it was confirmed that the oxygen functional groups were significantly reduced in the examples. For reference, the XPS spectra of graphene oxide and the reduced graphene oxide of Example a3-8 are shown in Fig. 2. Fig. 2(a) shows the XPS (C1s) spectrum of graphene oxide (GO), and Fig. 2(b) shows the XPS (C1s) spectrum of the reduced graphene oxide (rGO) of Example a3-8. Here, the XPS (C1s) spectrum indicates the region corresponding to the energy peak position of the 1s orbital of C among the XPS spectra. In Figs. 2(a) and (b), the raw data are indicated by ○, and the fitting results of the raw data are indicated by broken lines. The four peaks of the spectra (broken lines) in Figs. 2(a) and (b) are assigned to C-C / C=C (284.2 eV), C-O-C / C-OH (286.1 eV), C=O (287.4 eV), and COOH (288.6 eV), respectively.

[0067] (Evaluation) The transmittance, surface resistivity of the reduced graphene oxide film obtained above at a light wavelength of 550 nm were measured. The transmittance of light with a wavelength of 550 nm was measured using an ultraviolet-visible-infrared spectrophotometer V-550 (manufactured by JASCO Corporation) in accordance with JIS Z8722. The surface resistivity was measured using a four-probe resistivity measuring instrument Σ-5+ (manufactured by NPYES Co., Ltd.) in accordance with JIS K7194. The results are shown in Tables 1 to 15 and Figures 3 to 5. Figure 3 is a graph showing the correlation between the transmittance of light with a wavelength of 550 nm and the surface resistivity in the reduced graphene oxide films of Examples a1 to a6. Figure 4 is a graph showing the correlation between the transmittance of light with a wavelength of 550 nm and the surface resistivity in the reduced graphene oxide films of Examples b1 to b5. Figure 5 is a graph showing the correlation between the transmittance of light with a wavelength of 550 nm and the surface resistivity in the reduced graphene oxide films of Examples c1 to c4. In any of the graphs, the vertical axis represents the surface resistivity (Rs), and the horizontal axis represents the transmittance of light with a wavelength of 550 nm (Tt).

[0068] (Drop volume: 0.05 ml) [Table 1]

[0069] (Drop volume: 0.1 ml) [Table 2]

[0070] (Drop volume: 0.2 ml) [Table 3]

[0071] (Drop volume: 0.3 ml) [Table 4]

[0072] (Drop volume: 0.6 ml) [Table 5]

[0073] (Drop volume: 1.0 ml)

Table 6

[0074] (Preheating temperature: 90 °C)

Table 7

[0075] (Preheating temperature: 100 °C)

Table 8

[0076] (Preheating temperature: 120 °C)

Table 9

[0077] (Preheating temperature: 150 °C)

Table 10

[0078] (Preheating temperature: 200 °C)

Table 11

[0079] (Substrate: Soda lime slide glass)

Table 12

[0080] (Substrate: Quartz slide glass)

Table 13

[0081] (Substrate: Polyimide film)

Table 14

[0082] (Substrate: Polyethylene terephthalate film)

Table 15

[0083] (Comparative example) In the same manner as the method described in Non-Patent Document 1, an attempt was made to form a graphene oxide film using hydrogen iodide instead of hydrazine. Specifically, first, 0.2 ml of hydroiodic acid (concentration: about 1.6 g / ml, 55.0 to 58.0 mass%) and 10 ml of the aqueous dispersion of graphene oxide prepared in Preparation Example 1 above (graphene oxide content: 0.2 mg / ml) were mixed and stirred to prepare an aqueous dispersion containing graphene oxide and hydrogen iodide. Next, an attempt was made to spray the above aqueous dispersion onto a soda lime slide glass using an airbrush (nozzle diameter 0.5 mm, Mr. Hobby Procon Boy PS-290 trigger airbrush). However, immediately after the start of spraying, the spray nozzle of the spray gun became clogged and the spraying stopped, so that a reduced graphene oxide film could not be formed. This is presumably because fine particles of reduced graphene oxide were generated in the vicinity of the spray nozzle.

Claims

1. placing a substrate in a reducing atmosphere containing at least one of iodine and hydrogen iodide; spraying a dispersion of graphene oxide onto the substrate in the reducing atmosphere to reduce the graphene oxide and deposit reduced graphene oxide, which is a reduced form of the graphene oxide, on the substrate, the method for forming a reduced graphene oxide film comprising the above steps.

2. The method for forming a reduced graphene oxide film according to Claim 1, wherein the dispersion contains at least one of water and ethanol.

3. The method for forming a reduced graphene oxide film according to Claim 1 or 2, wherein the content of graphene oxide in the dispersion is 0.01 to 2 g / L.

4. The method for forming a reduced graphene oxide film according to Claim 1 or 2, wherein the reducing atmosphere is formed by heating a solution containing at least one of iodine and hydrogen iodide.

5. A reduced graphene oxide film having a light transmittance of 85 to 99% at a wavelength of 550 nm, a surface resistivity of 1500 to 60000 Ω / sq, and a thickness of 0.0005 to 0.1 μm.

6. An article comprising a substrate and the reduced graphene oxide film according to Claim 5 provided on the substrate.

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