JP5839571B2 - Method for producing graphene film doped with nitrogen atoms - Google Patents

Description

  The present invention relates to a method for producing a graphene film doped with nitrogen atoms, a graphene film doped with nitrogen atoms, and uses thereof.

Graphene is a planar substance composed of sp ² bonded carbon atoms filled in a honeycomb-like hexagonal lattice.

  In a narrow sense, graphene refers to a substance (monolayer graphene) having a single-layer hexagonal lattice structure. A structure in which graphene is stacked is called graphite. In a broad sense, graphene refers to a structure in which a small number of the above hexagonal lattice structures are stacked (few layer graphic structures).

  Further, graphene refers to a planar substance, but on the other hand, for example, a carbon nanotube, which is one of the allotropes of carbon atoms, can be regarded as cylindrical graphene.

  A single-layer graphene and a film having a structure in which a small number of hexagonal lattice structures are stacked (hereinafter collectively referred to as “graphene film”) has extremely high electron mobility, extremely low visible light absorption, and extremely high Due to its mechanical strength (for example, extremely high Young's modulus) and the like, it has attracted high attention as a new transparent electrode material.

  Conventionally, several types of methods have been proposed as methods for producing graphene films.

  In particular, a method of synthesizing a graphene film on a catalytic metal substrate by chemical vapor deposition (CVD) (hereinafter referred to as “CVD method”) is expected as a practical method.

  Further, in recent years, a graphene film doped with nitrogen atoms (hereinafter referred to as “N-doped graphene film”) has attracted attention. In particular, it has been reported that N-doped graphene films in which carbon atoms are substituted with nitrogen atoms can have three types of substitution modes (Non-Patent Document 1).

  N-doped graphene films are expected to be more conductive and stronger than pure graphene films. Therefore, the N-doped graphene film can be effectively used as, for example, an active material for an electricity storage device, a fuel cell electrode catalyst and a catalyst carrier, and a conductive thin film material for a display electrode.

  As a method for producing an N-doped graphene film, a silicon substrate (hereinafter referred to as a copper / silicon substrate) on which a copper thin film having a thickness of 25 nm is formed is used, and N-doped graphene is formed on the surface of the copper thin film by a CVD method. Methods for forming films have been reported. For example, when the temperature of the heat source is increased to 800 ° C. in a state where hydrogen and argon are flown as carrier gases inside a reaction vessel having a copper / silicon substrate located in the vicinity of the heat source, carbon is further added. A method of forming an N-doped graphene film on a copper foil by introducing methane as a source and ammonia as a nitrogen source respectively into a carrier gas flow and then quickly moving the copper / silicon substrate to a higher temperature region. It has been reported (Non-Patent Documents 2 and 3). At this time, a quartz tube is used as the reaction vessel.

Liuyan Zhao et al., Science, 2011, Vol. 333 no. 6045 pp. 999-1003 Jannik C.I. Meyer et al., Nature materials, 2011, 10, pp. 209-215 Dachen Wei et al., NANO LETTERS, 2009, Vol. 9 No. 5, pp. 1752-1758

  However, when the present inventors examined, in the method of manufacturing the conventional N-doped graphene film, an excessive amount of nitrogen source is necessary as compared with the amount necessary for calculation, so that the manufacturing efficiency is poor, and There was a problem that a nitrogen by-product that was not taken into the N-doped graphene film further reacted with a carbon source to generate a reaction by-product. In addition, ammonia is corrosive and has a problem that the reaction vessel is restricted.

  Accordingly, the present invention provides a method for producing an N-doped graphene film having superior production efficiency and a reduced amount of reaction by-products compared to conventional ones. Let it be an issue.

  The present inventors examined the cause of the deterioration of the production efficiency and the generation of reaction byproducts in the conventional method for producing an N-doped graphene film. As a result, in the conventional method, since the carbon source and the nitrogen source are mixed with each other in the gaseous state in the carrier gas flow and then provided on the substrate, both gases are completely mixed on the substrate. This is a non-uniform state, and as a result, only a part of the nitrogen source introduced into the carrier gas flow is actually taken into the N-doped graphene film. The present inventors have determined that this is the cause.

  The present invention has been completed by further research based on the above new findings. The gist of the present invention is shown below.

Item 1. A method for producing a graphene film doped with nitrogen atoms,
A solution containing a carbon source and a nitrogen source,
Introducing into the reaction vessel having a substrate inside by spraying,
A method comprising a step of forming a graphene film doped with nitrogen atoms on the surface of the substrate by chemical vapor deposition.
Item 2. Item 2. The method according to Item 1, wherein the carbon source is an organic solvent.
Item 3. Item 2. The method according to Item 1, wherein the carbon source is methanol.
Item 4. The nitrogen source is
Item 4. The compound according to any one of Items 1 to 3, which is at least one melamine derivative selected from the group consisting of a compound represented by the following formula (I) and an oligomer and polymer having a structural unit derived from the compound. Method

(In the formula, at least one of X ¹ , X ² and X ³ represents an amino group, and the other represents an NR ¹ R ² group (R ¹ and R ² are each independently a hydrogen atom (however, Not an atom) or an alkyl group having 1 to 10 carbon atoms (which may have an ether bond).
Item 5. Item 5. The method according to Item 4, wherein the solution contains 0.0005 to 1 wt% of the melamine derivative.
Item 6. Item 5. A graphene film doped with nitrogen atoms, obtainable by the method according to any one of Items 1 to 4.

  According to the production method of the present invention, an N-doped graphene film can be produced with high efficiency and while suppressing reaction byproducts.

It is drawing which showed the specific example of a mode that the manufacturing method of the N-doped graphene film of this invention is implemented. In addition, the arrow in a figure represents the direction through which carrier gas and a spray body (mist) flow. It is drawing which showed the specific example of a mode that the rapid cooling process in the manufacturing method of the N-doped graphene film of this invention is implemented. In addition, the arrow in a figure represents the direction through which carrier gas and a spray body (mist) flow. It is drawing which showed the specific example of a mode that the rapid cooling process in the manufacturing method of the N-doped graphene film of this invention is implemented. In addition, the arrow in a figure represents the direction through which carrier gas and a spray body (mist) flow. In an Example, it is a graph which shows the result of having measured the surface resistance value of the N-doped graphene film.

  In this specification, the “graphene film” means a single-layer graphene and a film having a structure in which a small number (for example, 2 to 20 layers) of the hexagonal lattice structure is laminated.

  In the present specification, “N-doped graphene film” means a graphene film doped with nitrogen atoms.

  In the present specification, “nitrogen atom doped” includes not only a state in which a carbon atom is substituted with a nitrogen atom but also a state in which a functional group containing a nitrogen atom is bonded to the carbon atom. .

  In this specification, the “CVD method” means a method of synthesizing a graphene film on a catalytic metal substrate by chemical vapor deposition (CVD).

1. Method for producing N-doped graphene film The method for producing N-doped graphene film of the present invention comprises:
A solution containing a carbon source and a nitrogen source,
Introducing into the reaction vessel having a substrate inside by spraying,
The method includes a step of forming a graphene film doped with nitrogen atoms by chemical vapor deposition on the surface of the substrate.

  As a CVD method, a known method can be used.

  Chemical vapor deposition includes thermal chemical vapor deposition and plasma vapor deposition, and combinations thereof.

  As a solution containing a carbon source and a nitrogen source (hereinafter sometimes referred to as “a spray solution”), a form in which a resinous nitrogen source is dissolved in a liquid carbon source is preferable. An organic solvent is mentioned as a liquid carbon source. By introducing such a spray solution into the reaction vessel by spraying, it is expected that the relative amount of the carbon source and the nitrogen source will be constant inside the reaction vessel. Since a gas atmosphere is obtained, a precursor for forming an N-doped graphene film is more easily formed, and an N-doped graphene film can be produced with higher efficiency and while suppressing reaction byproducts. Conceivable. Thus, the effect of the present invention that the relative amount of the carbon source and the nitrogen source can be made constant inside the reaction vessel is further improved by adjusting the ratio of the carbon source and the nitrogen source, etc. : N-doped graphene having a lower N ratio can be produced.

  Specific examples of the organic solvent as the carbon source used in the present invention include methanol, ethanol, 1-propanol, 2-propanol, toluene and xylene, and a mixture of two or more thereof. As the carbon source used in the present invention, methanol is preferable.

  Examples of the nitrogen source used in the present invention include melamine derivatives.

  Examples of the melamine derivative used in the present invention include at least one melamine derivative selected from the group consisting of a compound represented by the following formula (I), an oligomer having a structural unit derived from the compound, and a polymer. It is done.

(In the formula, at least one of X ¹ , X ² and X ³ represents an amino group, and the other represents an NR ¹ R ² group (R ¹ and R ² are each independently a hydrogen atom (however, Not an atom) or an alkyl group having 1 to 10 carbon atoms (which may have an ether bond).

  As the compound represented by the following formula (I), alkylated melamine and etherified melamine are more preferable.

  In the above, examples of the alkylated melamine include methylated melamine, ethylated melamine, n-propylated melamine, and isopropylated melamine.

  In the above, examples of the etherified melamine include methyl etherified melamine, ethyl etherified melamine, n-propyl etherified melamine, and isopropyl etherified melamine.

  Although it does not specifically limit as a melamine derivative used by this invention, When using an organic solvent as a carbon source, what melt | dissolves in an organic solvent is preferable. The melamine derivative used in the present invention is particularly preferably a melamine derivative that is easily dissolved in many organic solvents. Examples of such a melamine derivative include methylated melamine.

  The concentration of the melamine derivative in the spray solution is preferably 0.0005 to 1% by weight, and more preferably 0.001 to 0.5% by weight. When the concentration is 0.0005 to 1% by weight, it is preferable in that generation of nanoparticles is suppressed. When the concentration is 1% by weight or less, it is preferable in that the unreacted nitrogen source is less likely to be carbonized, and nitrogen carbide is less likely to adhere to the inner wall of the N-doped graphene film or reaction vessel that is the final product. .

  The spray solution may further contain other components within the range where the effects of the present invention are exhibited. In this case, the other components are not particularly limited, and examples thereof include water.

  When the spray solution contains water, it is not particularly limited. However, the organic solvent contains water to such an extent that a decomposition gas generated from an unreacted carbon source or an unreacted nitrogen source can be appropriately oxidized by an aqueous activation reaction or the like. It is preferable. However, if the amount of water contained in the organic solvent is large, the final product, the N-doped graphene film itself, is oxidized, so the size of the reaction vessel, the flow rate of the atmospheric gas, the heating temperature, the heating time, etc. It is preferable to appropriately adjust the amount of water according to the reaction conditions.

  The reaction vessel has a substrate inside. An N-doped graphene film is synthesized on the surface of the substrate by heat treating the carbon source and the nitrogen source.

  The substrate used in the present invention is not particularly limited as long as it can form graphene on the surface by a CVD method, and for example, a metal foil can be used. Although it does not specifically limit as thickness of metal foil, 10-50 micrometers is preferable, 15-40 micrometers is more preferable, 20-30 micrometers is further more preferable.

  Examples of the metal constituting the metal foil include copper, nickel, cobalt, iron, platinum, gold, aluminum, chromium, magnesium, manganese, molybdenum, rhodium, silicon, tantalum, titanium, tungsten, uranium, vanadium and zirconium, and Among these, two or more kinds of alloys are mentioned. The metal constituting the metal foil is preferably copper and nickel, and alloys thereof, and more preferably copper.

  The shape of the reaction vessel can be appropriately selected within the range where the effects of the present invention are exhibited. Although not particularly limited, for example, a prismatic shape or a cylindrical shape.

  The internal volume of the reaction vessel can be adjusted as appropriate within the range where the effects of the present invention are exhibited. With respect to the upper limit of the volume, for example, a size that allows a large difference in temperature to be observed in the region where the base material is disposed, among the inside of the reaction vessel is allowed.

  The material of the reaction vessel can be appropriately selected within the range in which the effect of the present invention is exhibited. Although it does not specifically limit, For example, quartz, SUS inconel, an alumina, etc. are mentioned. Quartz is preferable as the material of the reaction vessel in terms of particularly high heat resistance, small thermal expansion, excellent workability, and cost.

  The distance from the location where the spray solution is sprayed to the surface of the substrate can be set as appropriate within the range where the effects of the present invention are exhibited. Specifically, the state of the spray body (mist) reaching the substrate surface is important for the manifestation of the effects of the present invention, and this is influenced by the spray amount and the cross-sectional area of the reaction container in addition to the above distance. Therefore, all elements can be set as appropriate.

  During the formation of the N-doped graphene film on the surface of the substrate, at least the region near the substrate in the reaction vessel is usually 600 to 1500 ° C., preferably 800 to 1200, depending on the heat source provided outside the reaction vessel. It is kept at 900C, more preferably 900-1000C.

  Although it does not specifically limit as a heat source, For example, an electric furnace etc. are mentioned. Although not particularly limited, a mantle heater (jacket heater) or the like can be used as a heat source. Further, when the reaction vessel is cylindrical, a tubular electric furnace can be used as a heat source. Commercially available mantle heaters and tubular electric furnaces can be used.

  Spray introduction of the spray solution into the reaction vessel can be performed in a state where a carrier gas is allowed to flow in the reaction vessel. The reaction vessel may have a gas inlet for introducing a carrier gas into the reaction vessel.

  The atmospheric gas (including the carrier gas) used when forming the N-doped graphene film is not particularly limited, but nitrogen, argon and hydrogen, and a mixed gas thereof are preferable. In addition, a hydrocarbon gas may be added to the atmospheric gas in order to increase the growth rate of graphene. Examples of the hydrocarbon gas include methane gas, ethylene gas, acetylene gas, and mixed gas thereof.

  An N-doped graphene film may be formed while evacuating. When the N-doped graphene film is formed while exhausting, the reaction vessel may have an exhaust port. The exhaust port is not particularly limited. For example, the exhaust port may be provided on the side opposite to the means for spraying and introducing the spray solution into the reaction vessel.

  The means for introducing the spray solution by spraying it into the reaction vessel is not particularly limited, and for example, a commonly used spray can be used. In addition, by using an ultrasonic atomizer as a means for introducing by spraying, a spray body (mist) having uniform droplets can be obtained, which makes it possible to obtain a carbon source and nitrogen as compared with the case of using only a normal spray. This is preferable because the source is supplied to the surface of the substrate in a more uniformly mixed state. When using an ultrasonic atomizer, for example, in a state where a carrier gas is flowed in the reaction vessel, the spray body is introduced into the reaction vessel using the ultrasonic atomizer at a position upstream of the carrier gas flow with respect to the substrate. As a result, the spray body can be supplied to the substrate surface in a carrier gas flow (FIG. 1).

  The installation direction during use of the reaction vessel is not particularly limited, but when the reaction vessel is prismatic or cylindrical, a direction in which the major axis direction is parallel to the surface of the substrate is desirable.

  Prior to spray introduction of the spray solution into the reaction vessel, the spray solution may be kept at a specific temperature in advance. The holding temperature in this case is preferably −10 to 70 ° C., more preferably 0 to 50 ° C., and further preferably 10 to 40 ° C.

  The reaction container may have a preheater in order to maintain the spray solution at a specific temperature in advance before spraying the spray solution into the reaction container. The preheater may be further connected to a spray supply device.

  In order to form the N-doped graphene film on the surface of the substrate, although it depends on other conditions, it is usually several seconds to several hours, preferably 1 to 10 minutes, more preferably 1 to 10 minutes after introducing the spray solution. It takes 2 minutes. The temperature of the heat source, the amount of spray solution sprayed per unit time, the distance from the spray solution spraying location to the substrate, the volume in the reaction vessel, etc. affect the time required to form the N-doped graphene film give.

  After forming the N-doped graphene film, the metal foil is cooled. In this case, natural cooling (for example, 10 to 20 ° C. decrease / 20 minutes) may be employed, or rapid cooling (for example, 100 to 500 ° C. decrease / 10 seconds) may be employed. The rapid cooling is not particularly limited, but can be performed, for example, by moving the substrate to a region sufficiently away from the heat source in the reaction vessel (FIG. 2 or FIG. 3). In particular, when nickel foil is used as the substrate, it can be expected that the quality of the graphene film is improved by rapid cooling.

After forming the N-doped graphene film, the N-doped graphene film can be transferred onto any substrate. Although not particularly limited, examples of the transfer method of the N-doped graphene film include a method comprising the following steps.
(Step 1) An N-doped graphene film is formed on the copper foil.
(Step 2) A support film for holding the N-doped graphene film is bonded to the surface of the N-doped graphene film.
(Step 3) The copper foil is removed using an etching solution.
(Step 4) The N-doped graphene film held in the support film obtained in Step 3 is transferred to the target substrate.
(Step 5) The support film is removed.

By transferring in this way, a large-area N-doped graphene film can be placed on any substrate. In order to synthesize a large-area N-doped graphene film at a low cost, or to continuously synthesize an N-doped graphene film at a low cost, it is preferable to employ a so-called roll-to-roll method. . In the roll-to-roll method, it is preferable that the substrate has a metal foil that can be wound and unwound.

  The state of nitrogen and the doping amount in the N-doped graphene film obtained in the present invention can be appropriately examined by elemental analysis, CNH analysis, X-ray photoelectron spectroscopy, and the like. In addition, the change in the band structure of graphene can be confirmed by the wavelength shift at the bottom of the transmission spectrum measured by an ultraviolet-visible spectrophotometer.

  In the present invention, an N-doped graphene film having a C: N ratio smaller than the conventional one can be obtained by using a very small amount of nitrogen source. The C: N ratio in the N-doped graphene film obtained in the present invention can be calculated from the addition amount of the carbon source and the nitrogen source on the assumption that the reaction efficiency is 100%. When the addition amount is unknown, the C: N ratio in the N-doped graphene film that can be obtained in the present invention is defined as follows. Assuming that the detection limit of C: N ratio that can be measured by CNH analysis is 0.001%, when N-doped graphene film is measured by CNH analysis and N is not detected, C: The N ratio is assumed to be 0.001% or less.

  Further, the crystallinity of the N-doped graphene film can be appropriately examined by Raman scattering spectroscopy or surface resistance measurement.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

Example 1
A substrate in which a copper foil having a length of 20 mm, a width of 20 mm, and a thickness of 20 μm was placed on a quartz plate having a length of 80 mm, a width of 20 mm, and a thickness of 1 mm was used as a substrate in the CVD method.

  A quartz tube placed in a tubular electric furnace was used as a reaction furnace, and the substrate was placed in the center of the reaction furnace. 0.001 g of methylated melamine (trade name MW-30, manufactured by Sanwa Chemical Co., Ltd.) is added to 99.999 g of methanol, and treated with an ultrasonic cleaner for 10 minutes to obtain a solution in which methylated melamine is dissolved in methanol. It was. After raising the temperature of the tubular electric furnace to 930 ° C. while flowing nitrogen gas, the solution was mixed with nitrogen gas using an ultrasonic atomizer, and the reactor was reacted at 0.4 mL / min and gas at 1 L / min, respectively. Introduced in. The reaction time was 2 minutes. Thereafter, the substrate is rapidly cooled to room temperature by moving the substrate to one end of the quartz tube sufficiently away from the tubular electric furnace that has generated heat from the central portion in the quartz tube, and N− formed on the substrate surface. A doped graphene film was obtained. This was transferred to a quartz substrate, and the surface resistance was measured.

Example 2
Methylated melamine (trade name: MW-30, manufactured by Sanwa Chemical Co., Ltd.) 0.005 g was added to 99.995 g of methanol, treated with an ultrasonic cleaner for 10 minutes, and a solution of methylated melamine dissolved in methanol was used as a raw material. It was. The rest is the same as in Example 1.

Example 3
A solution prepared by adding 0.01 g of methylated melamine (trade name MW-30, manufactured by Sanwa Chemical Co., Ltd.) to 99.99 g of methanol and treating it with an ultrasonic cleaner for 10 minutes to dissolve methylated melamine in methanol It was. The rest is the same as in Example 1.

Example 4
Methylated melamine (trade name: MW-30, manufactured by Sanwa Chemical Co., Ltd.) 0.1 g was added to 99.9 g of methanol, treated with an ultrasonic cleaner for 10 minutes, and a solution obtained by dissolving methylated melamine in methanol was used as a raw material. It was. The rest is the same as in Example 1.

Example 5
Methylated melamine (trade name: MW-30, manufactured by Sanwa Chemical Co., Ltd.) (0.5 g) was added to 99.5 g of methanol, treated with an ultrasonic cleaner for 10 minutes, and a solution obtained by dissolving methylated melamine in methanol was used as a raw material. It was. The rest is the same as in Example 1.

Comparative Example 1
Methanol was used as a raw material. The rest is the same as in Example 1.

Reference example 2 g of methylated melamine (trade name: MW-30, manufactured by Sanwa Chemical Co., Ltd.) was added to 98.0 g of methanol and treated with an ultrasonic cleaner for 10 minutes to dissolve methylated melamine in methanol. The solution was used as a raw material. The rest is the same as in Example 1.

Comparative Example 2
In addition to the reaction vessel, a resin heating furnace was provided, and a boat containing 5 g of melamine resin was placed therein and heated to 600 ° C. so that the resin decomposition gas and methanol flowed to the reaction vessel. The rest is the same as in Example 1. As a result, many by-products were confirmed in the resin heating furnace and the reaction vessel. In addition, the synthesized graphene was low in crystallinity, and the graphene film was divided when the copper foil was etched, and could not be transferred.

Test example [transfer method]
A commercially available high-adhesion easily peelable tape (eg, Selfa (trade name), Sekisui Chemical Co., Ltd.) was attached to the surface of the substrate formed with the N-doped graphene film adjacent to the quartz plate. Next, a 2 wt% polymethyl methacrylate-acetone solution and then a 5 wt% polymethyl methacrylate-acetone solution were respectively applied by spin coating on the surface of the substrate (the side opposite to the surface on which the high-adhesion easy-peeling tape was affixed). Then, the solution was dried to form a support film.

  The high-adhesion easy-release tape was peeled from the substrate on which the N-doped graphene film was formed by placing the substrate on which the high-adhesion easy-release tape was affixed on a hot plate.

  The copper foil was melt | dissolved by making the back surface (surface on which the highly adhesive easy peeling tape was affixed) contacted the 1M ferric nitrate aqueous solution of the board | substrate which the N-doped graphene film formed. After the copper foil was dissolved, it was washed with a water bath and scraped off with a quartz substrate. After drying the sample, the support film was dissolved with acetone, washed with water and dried, and then the surface resistance value was measured.

[Measurement of surface resistance]
Using a surface resistance meter (trade name: Loresta-EP) manufactured by MITSUBISHI CHEMICAL ANALYTECH, it was measured by the 4-probe method.
The measured surface resistance value R is shown in FIG. 4 as a value R / R0 divided by the surface resistance value R0 of the graphene film (Comparative Example 1) when methanol is used as a raw material. The X axis shows the addition ratio of methylated melamine in the spray solution.

  As a result, when the addition ratio of methylated melamine in the spray solution is 0.0005 to 1% by weight, a preferable surface resistance value is obtained, and when the addition ratio is 0.001 to 0.5% by weight. It was found that a more preferable surface resistance value can be obtained.

1 reaction container 2 substrate 3 spray body (mist)
4 Atomizer 5 Heat source 6 Flow meter 7 Carrier gas container

Claims (5)

A method for producing a graphene film doped with nitrogen atoms,
A solution in which a resinous nitrogen source is dissolved in a liquid carbon source ,
Introducing into the reaction vessel having a substrate inside by spraying,
A method comprising a step of forming a graphene film doped with nitrogen atoms on the surface of the substrate by chemical vapor deposition. The method of claim 1, wherein the carbon source is an organic solvent. The method of claim 1, wherein the carbon source is methanol. The nitrogen source is
The compound represented by the following formula (I), and at least one melamine derivative selected from the group consisting of an oligomer and a polymer having a structural unit derived from the compound, according to any one of claims 1 to 3. the method of

(In the formula, at least one of X ¹ , X ² and X ³ represents an amino group, and the other represents an NR ¹ R ² group (R ¹ and R ² are each independently a hydrogen atom (however, Not an atom) or an alkyl group having 1 to 10 carbon atoms (which may have an ether bond).
). The method according to claim 4, wherein the solution contains 0.0005 to 1% by weight of the melamine derivative.

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