JP5777701B2 - Method for producing two-dimensional sandwich nanomaterials based on graphene - Google Patents

Description

  The present invention relates to a method for producing two-dimensional (2-D) nanomaterials and sandwich nanomaterials coated with carbon, metal or metal oxide based on graphene or graphene oxide, and sandwich materials. The present invention also relates to a method of using a two-dimensional sandwich nanomaterial as a template for producing a 2-D sandwich material, using the sandwich material in a catalyst, a sensor, a primary and secondary electrochemical cell, and a fuel cell. And a method for producing a single layer of graphene in a 2-D sandwich nanomaterial according to the present invention.

A two-dimensional (2-D) nanomaterial is basically a material that is not finite in two dimensions, but whose third dimension (thickness) is limited to the nanoscale. This makes the ratio of length to thickness very large in most such particulate materials. Graphene is a 2-D nanomaterial in that it has a planar layer of 6-membered rings in which 6 carbon atoms are sp ² covalently bonded. Graphite is composed of a plurality of layers of these graphenes. Graphene has extremely high mechanical strength and high conductivity. However, graphene and functional two-dimensional nanomaterials based on graphene are difficult to produce graphene, and their application is hindered.

  Graphene first applies an adhesive strip to highly oriented pyrolytic graphite (HOPG), which is then peeled off with the graphite to adhere several layers of graphene to the adhesive strip, which is then applied to the silicon wafer. Manufactured by transferring. This method is very time consuming and has a low yield, but is still used today to obtain very high purity graphene particles.

  Another method is chemical vapor deposition (CVD), in which the carbon source is evaporated and deposited on the catalyst support. This method produces graphene particles stably, but does not cause suspension of “free” particles of graphene in the medium. Graphene can be obtained by epitaxial growth on a metal substrate. There is also a method of generating graphene by heating SiC to a temperature exceeding 1100 ° C. Both of these methods produce surface-coated graphene, but there are no “free” particles of graphene.

  Another method for producing graphene particles is solution exfoliation of graphite. In this method, graphite is exfoliated into a graphene particle in an organic solvent such as N-methylpyrrolidone by positive interaction between the solvent and the graphite surface. For this purpose, a special solvent is required, and there is a problem that, for example, a treatment such as application to another metal layer is necessary to make graphene functional. Furthermore, since the graphene particles tend to accumulate again quickly, the yield of the monolayer is only low.

Graphene particles can be obtained by chemical reduction of graphene oxide particles in an aqueous suspension. However, this method can leave a certain proportion of oxidized groups in the graphene. Although graphene oxide can be readily dispersed in water due to the large number of oxygen-containing groups, the resulting anionic properties make graphene oxide almost incompatible with inorganic compounds such as SiO ₂ . Furthermore, a graphene suspension produced by reduction of an aqueous graphene oxide suspension has low dispersibility in water and therefore aggregates, making it very difficult to obtain individual graphene particles.

  Graphene oxide can also be converted to graphene by thermal means (Aksay, Chem. Mater. 2007, 19, 4396-4404). However, graphene particles become agglomerated at high temperatures, and it is difficult to obtain individual graphene particle groups.

  Nevertheless, due to the good properties of graphene, such as its high electron mobility, very good conductivity is obtained and the quantum Hall effect occurs at room temperature, thus making the graphene function continuous.

  Patent Document 1 discloses a method of manufacturing a nanocomposite element based on graphene and a metal oxide. In this method, graphite flakes are chemically oxidized, and the resulting graphite oxide is exfoliated by rapid thermal diffusion and partially converted into graphene. The exfoliated graphene particles are used for the production of an aqueous dispersion containing sodium dodecyl sulfate (for particle stabilization). A metal oxide precursor is added to the dispersion and evaporated onto the dispersed graphene particles to form a nanocomposite device material. With this manufacturing method, the graphene particles have a carbon / oxygen ratio of 10 to 500. Oxygen atoms in the graphene particles make it somewhat difficult to adsorb the anionic surfactant on the surface.

  Graphene oxide is obtained by oxidation of graphene and graphite, and has a state in which carbon atoms are bonded to a six-membered ring in one layer, and includes an oxygen-containing group. Graphene oxide is equally useful as a starting point for the production of functional two-dimensional nanomaterials.

WO2010 / 014215A2

“Polyurethane”, Kunststoff-Handbuch, Vol. 7, 2nd edition, 1983, Dr. Ed. Guerter Oertel, Volume 7, Third Edition, 1993, Dr. Guenter Otel, Carl-Hanser-Verlag, Munich / Vienn

  However, there is a need for a method for producing graphene and a method for producing functional graphene and graphene oxide to avoid the above-mentioned drawbacks of the prior art, and good performance characteristics based on graphene and graphene oxide are present. A 2-D nanomaterial is required.

  Accordingly, an object of the present invention is to prepare a method for producing graphene particles and functional graphene particles and graphene oxide particles in a relatively simple and high-yield manner. Furthermore, it is an object of the present invention to prepare functional 2-D nanomaterials based on graphene and graphene oxide, which have particularly good performance characteristics, for example in the cathode material of lithium ion secondary batteries.

  It has been found that the above object is achieved according to the present invention by the following method.

This method
(A)
(A1) Graphene oxide particles, water, and a mixture containing one or more cationic surfactants and / or nonionic surfactants, or (a2) one or more solvents useful for solution exfoliation of graphene particles and graphite And preparing a mixture comprising one or more cationic surfactants and / or nonionic surfactants,
(B) adding one or more sol precursor compounds to the mixture obtained from step (a);
(C) the step of reacting the mixture obtained from step (b) in a sol / gel method to form a gel from one or more sol precursor compounds into graphene oxide particles or graphene particles,
(D) removing the one or more surfactants, and (e) optionally heating the gel-coated graphene oxide particles to 500 ° C. or higher for 1 minute or longer in an inert gas atmosphere, Reducing graphene oxide to graphene,
Is a method for producing a two-dimensional sandwich nanomaterial.

In a preferred embodiment, the one or more sol precursor mixtures are selected from SiO ₂ precursor mixtures. When the treatment is performed according to this embodiment, according to the present invention, in addition to the steps (a) to (d), the following (f) SiO ₂ -coated graphene oxide particles or SiO ₂ -coated graphene particles, Impregnating one or more precursor compounds selected from the group consisting of metal oxide precursor compounds, metal precursor compounds, and carbon precursor compounds;
(G) a step of converting one or more precursor compounds to a corresponding metal oxide, a corresponding metal, or carbon, and (h) a step of removing SiO ₂ from each graphene oxide particle or graphene particle,
A method is provided for producing a 2-D sandwich nanomaterial having:

  The present invention also provides a 2D sandwich nanomaterial obtained according to the method of the present invention, a method of using the material as a template for producing a nanolayer material, the material as a catalyst, a sensor, a capacitor, primary and secondary electrochemistry. A cell, a method for use as a fuel cell, and a catalyst, sensor, capacitor, primary and secondary electrochemical cell, and fuel cell comprising the two-dimensional sandwich nanomaterial of the present invention are provided.

Furthermore, the present invention is a method of using the 2D sandwich nanomaterial of the present invention to produce graphene particles, and a method of producing graphene particles having the above steps (a) to (d), wherein the step (b ) One or more sol precursor compounds in the same manner are selected from SiO ₂ precursor compounds,
(H) a step of removing SiO ₂ ;
And a manufacturing method is prepared that executes step (e) when a mixture according to (a1) is provided in step (a).

The method for producing 2D nanomaterials and 2D sandwich nanomaterials based on graphene or graphene oxide according to the present invention is simple to perform, has a relatively high throughput, and yields of coated 2D nanomaterials Becomes higher. These coated 2D nanomaterials can be obtained using a wide variety of different coating methods. Even when impregnation and removal by nano-casting are repeated, coating is possible although not directly obtained. For example, nanocasting is used for the production of graphene particles using mesoporous Co ₃ O ₄ by using 2D nanomaterials formed from graphene coated with SiO ₂ . Other 2D nanomaterials coated with metals or metal oxides can be obtained in a similar manner. For example, Sn, Ge, Co, SnO 2, TiO 2, Fe 2 O 3, and a 2D nanomaterials coated with Fe ₃ O _4. In particular, in the embodiment of the invention in which a mixture according to (a1) is provided in step (a) and graphite oxide is converted to graphene in step (b), graphene (a relatively inexpensive and widely used starting material) A simple route to coated 2D nanomaterials based on (obtained by processing graphene oxide) is represented.

  The 2D sandwich nanomaterial obtained according to the present invention has a very large length to thickness ratio, a very uniformly formed mesoporous structure and a very high specific surface area. This is due to the surfactant molecules used in step (a), and the mesoporous structure can be changed according to the use of various surfactants. The 2-D sandwich nanomaterial obtained by the method of the present invention has very good characteristics when, for example, the graphene particles of the present invention coated with mesoporous carbon are used as an anode material in a lithium ion secondary battery. By exhibiting, it has good characteristics.

  The present invention is described in detail as follows.

In this specification, graphite means carbon which is a plurality of planes and layers formed by a six-membered ring in which carbon atoms are bonded to each other by sp ² -covalent bonds to form a plurality of planes. To be understood.

Strictly speaking, “graphene” is a single carbon layer in a graphite structure, that is, a single layer in which a six-membered ring in which six carbon atoms are bonded in a hexagonal shape by sp ² -covalent bonds is arranged. As understood.

For the purposes of the present invention, “graphene” refers to a single layer of six or fewer layers in which six carbon atoms are arranged in a hexagonal shape by sp ² -covalent bonds with each other. It means a material to be formed, preferably 5 layers or less, more preferably 2 layers or less, and still more preferably 1 layer or less.

“Graphite oxide” means a three-dimensional structure composed of a plurality of layers. The plurality of layers are each composed of C ₆ -rings partially functionalized with carbonyl, carboxyl, alcohol, and epoxy groups. These individual layers are no longer planar in the graphite, but project in a zig-zag manner entirely or partly from the plane, depending on their degree of oxidation.

“Graphite oxide” for the purposes of the present invention comprises 10 layers formed from C ₆ -rings affected by oxygen functional groups such as epoxy groups, alcohol groups, carboxyl groups, and / or carbonyl groups. Hereinafter, it is understood to mean a material formed preferably of 5 layers or less, more preferably 2 layers or less, and still more preferably a single layer.

  In the present invention, “particle” is used as a general term for graphene oxide particles and graphene particles.

  In the present invention, the “two-dimensional nanomaterial and sandwich element” is infinite in the two-dimensional direction in principle, but is limited to a size in the range of 0.3 nm to 500 nm even if an arbitrary coating is included in the three-dimensional direction. Means platelet-shaped particles. This dimension is measured with an electron microscope. The sandwich particles of the present invention based on graphene and graphene oxide may be composed of one or more layers having a sandwich-like layered structure in which the coating / graphene or graphene oxide coating is continuously coated on the upper surface and the bottom surface thereof. .

Step a) of the method of the invention comprises
(A1) Graphene oxide particles, water, and a mixture containing one or more cationic surfactants and / or nonionic surfactants, or (a2) one or more solvents useful for solution exfoliation of graphene particles and graphite And preparing a mixture comprising one or more cationic surfactants and / or nonionic surfactants.

  Graphite oxide particles are usually used to prepare a mixture according to step (a1). Methods for producing graphite oxide particles are known by those skilled in the art. Usually, graphite oxide is produced by oxidation of graphite. Oxidation causes oxygen atoms to be embedded in the graphite, producing primary alcohols, epoxy groups, carbonyl groups, and carboxyl groups. These groups extend into the gaps between the individual layers, making it easier to separate the layers from each other. In addition, the oxide layer of graphite is more hydrophilic and easily dispersed in water because it contains oxygen-containing groups.

  Methods for producing graphite oxide are known by those skilled in the art. Usually, this production method includes a step of treating graphite with an oxidizing agent and an acid (more preferably a strong acid). The oxidizing agents used are more preferably chlorates and permanganates, with sulfuric acid and nitric acid being particularly used as acids.

  "L. Staudenmeier, Ber. Dt. Chem. Ges. 31, (1898), 1481, and L. Staudenmeier, Ber. Dt. Chem. Ges. 32, (1899), 1394" includes fuming nitric acid and A method for producing graphite oxide (referred to as graphic acid in this document) by reacting with potassium chlorate and potassium permanganate in the presence of concentrated sulfuric acid is disclosed.

  In “WS Hummers, RE Offeman, J. Am. Chem. Soc. 80 (1958), 1339”, graphite is reacted with potassium chlorate and potassium permanganate in the presence of sulfuric acid. Discloses a method for producing graphite oxide.

  Further, expansive graphite may be used as a precursor for producing graphite oxide. In this case, the graphite is expanded in the first step. Then, the obtained product is placed on, for example, a ball mill. The last step is the chemical modification described above, either by thermal oxidation or oxidation in the presence of sulfuric acid.

  Furthermore, the mixture comprises water and one or more cationic surfactants and / or nonionic surfactants. Suitable surfactants will be described later.

  When the mixture of (a1) is prepared for treatment from graphite oxide particles, the graphite oxide particles are at least partially exfoliated to graphene oxide particles, thus the mixture will contain graphene oxide particles. .

In order to prepare the mixture of (a2), the graphite particles are usually suspended in one or more suitable solvents. In this method, the graphite particles are solution exfoliated in an organic solvent and separated into individual layers, resulting in a suspension of graphene particles in one or more aprotic solvents. This step is realized using a solvent having a surface energy equal to that of graphene. When the surface energy of the solvent is 55 to 90 mJ / m ² , exfoliation of the graphite particles (Hernandez et al., ArXiV: 0805.2850 v1) on the graphene particles is performed reliably. Suitable solvents are, for example, N, N-dimethylacetamide, γ-butyrolactone, 1,3-dimethyl-2-imidazolidinone, and N-methylpyrrolidone.

In addition, solvents useful for solution stripping of graphite include dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, dimethylacetamide, and cyclohexane.
In the present invention, it is preferable to use a solvent selected from the group comprising N-methyl-pyrrolidone, dimethylformamide, dimethylsulfoxide, tetrahydrofuran, dimethylacetamide, and cyclohexane, and dimethylformamide is particularly preferable.

  Pyrographite, electrographite, and expanded graphite are particularly preferred, but naturally occurring graphite and artificially produced graphite can also be used.

  Furthermore, the mixture provided in (a) according to (a1) or (a2) comprises one or more cationic and / or nonionic surfactants.

The cationic surfactant is preferably selected from the group of quaternary ammonium compounds, more preferably C _n H _{2n + 1} N (R) ₃ Hal (where n = 12, 14, 16, and 18, Hal = Cl and Br, and R = CH ₃ or C ₂ H ₅ , R may be the same or different.), Particularly preferably cetyltrimethylammonium chloride, cetyltrimethylammonium bromide, and cetyltriethylammonium It is bromide.

One or more non-ionic surfactants are preferably, C ₂ -C ₄ comprising ethylene oxide - is selected from the group of alkylene oxide block copolymers. This copolymer is commercially available, for example, under the name Pluronic® from BASF SE.

  The presence of one or more cationic and / or nonionic surfactants avoids the problem of incompatibility between graphene / graphene oxide and inorganic materials and the problem of aggregation. Cationic and / or nonionic surfactants are adsorbed electrostatically on the surface of graphene oxide that is strongly negatively charged, or adsorbed on the surface of graphene by the interaction of π electrons in the graphene structure. Then, the cationic and / or nonionic surfactant collects in a regular microstructure on the top and bottom surfaces of the surface of the graphene or graphene oxide particles. For example, cetyltrimethylammonium bromide adsorbed on graphene oxide particles forms tubular micelles constituting mesoporous of about 2 nm size after coating.

  One or more solvents useful for preparing a mixture of (a1) comprising graphene oxide particles, water, and one or more cationic and / or nonionic surfactants, or for solution stripping of graphene particles, graphite , And a mixture starting from graphite oxide or graphite particles to prepare a mixture of (a2) comprising cationic and / or nonionic surfactants, respectively, usually exfoliation of graphite oxide particles or graphite particles respectively. To be functional and improved, energy is processed as input. Such energy input is performed using ultrasound, agitation, vibration, and other methods known by those skilled in the art. For example, a stirring device such as an Ultra-Turrax (registered trademark) stirrer, a pulverizing device, and a dispersing device may be those known by those skilled in the art.

  In order to prepare the mixture of (a1), in the present invention, 0.005 to 5% by mass of graphite oxide particles, more preferably 0.01 to 5% by mass of graphite oxide particles, more preferably, based on the total mass. It is preferable that the process proceeds from a mixture containing 0.01 to 2% by weight of graphite oxide particles. The concentration of the one or more cationic and / or nonionic surfactants is preferably 0.1 to 10% by weight, more preferably 0.2 to 5% by weight, most preferably relative to the total weight of the mixture. Is 0.2-1 mass%.

  In order to prepare the mixture of (a2), in the present invention, 0.01% by mass of graphite particles, more preferably 0.5% by mass of graphite particles, and further preferably 1% by mass of graphite particles with respect to the total mass. It is preferred that the process proceeds from a mixture comprising This mixture is preferably 0.1 to 10% by weight, more preferably 0.2 to 5% by weight and most preferably 0.2 to 1% by weight of one or more cations, based on the total weight of the mixture. And / or nonionic surfactants.

  When not all graphite oxide particles or graphite particles are exfoliated into a single layer of graphene particles, in the step of preparing the mixture, at least some unexfoliated particles are carefully centrifuged, etc. May be removed.

  According to the invention, the mixture provided in step (a1) is preferably from 0.005 to 5% by weight of graphene, more preferably from 0.01 to 5% by weight with respect to the total weight. Graphene particles comprising oxide particles and provided in step (a2) are preferably 0.001-5% by weight, more preferably 0.01-1% by weight, based on the total weight including.

  Step (b) in the method of the present invention includes the step of adding one or more sol precursor compounds to the mixture obtained in step (a). "Sol precursor compound" means a compound that takes a so-called sol form under conditions that appear in a particular mixture. Here, “sol” should be understood as a term used in a “sol-gel method” known by those skilled in the art. In the “sol-gel method”, the sol precursor is first converted to a sol and then converted to a gel. The sol-gel method is described in, for example, “W. Stober et al., J. Colloid Interf. Sci 26 (1968), page 62”.

In the present invention, the one or more sol precursor compounds are converted into SiO ₂ precursor compounds, ZrO ₂ precursor compounds, TiO ₂ precursor compounds, CeO ₂ precursor compounds, Al ₂ O ₃ precursor compounds, Fe ₂ O ₃ precursors. Body compound, Fe ₃ O ₄ precursor compound, MgO precursor compound, ZnO precursor compound, chromium oxide precursor compound, Co ₂ O ₃ precursor compound, molybdenum oxide precursor compound, tungsten oxide precursor compound It is preferably selected from the group consisting of a precursor compound of hafnium oxide, a Y ₂ O ₃ precursor compound, a water-soluble crosslinked polymer, and a polymer precursor.

According to the invention, the metal alkoxide is preferably selected from Me (OR) _n . However, n = 2 for Me = Zn, Mg, n = 3 for Me = Al, Y, Fe, Cr, Co, Me = Si, Zr, Ti, Ce, Mo, W, Hf n = 4 and R are C ₁ -C ₈ -alkyl, which may be substituted with one or more OH groups and may be the same or different from each other.

Very particularly preferably, the one or more sol precursor compounds are selected from water glass and Si (OR) ₄ . However, in Si (OR) ₄ , R is HCH ₃ , C ₂ H ₅ , C ₂ H ₄ OH, n-C ₃ H ₇ , i-C ₃ H ₇ , n-C ₄ H ₉ , and t- C ₄ H _9, which may be the same or different.

  According to the present invention, it is preferred that the soluble crosslinkable polymer and polymer precursor are selected from melamine formaldehyde resin precursor and resorcinol-formaldehyde resin precursor.

  The one or more sol precursor compounds in the step (b) are usually slowly added to the mixture obtained in the step (a) to be in a liquid state. This mixture may be added to the solution or without a solvent. The concentration of the one or more sol precursor compounds added in the step (b) is usually 0.1 to 10% by mass with respect to the graphene oxide particles or graphene particles present in the mixture (a), preferably It is 0.2-5 mass%, More preferably, it is 0.2-1%.

  Depending on the sol precursor compound used, a catalyst for sol and / or a catalyst for gel formation may be added during step (b) such as acid or base or before step (b). .

  Surfactant molecules that are adsorbed on graphene oxide particles or graphene particles and aggregate together to form a mesoporous structure are produced by controlled nucleation from one or more sol precursor compounds in the graphene oxide particles or graphene particles and Form a molecular template for sol or gel growth.

  The step (c) in the method of the present invention includes a step of reacting the mixture obtained in the step (b) by a sol-gel method. The gel is obtained by adsorbing the surfactant molecules on the graphene oxide or the graphene particles. Therefore, it is deposited on the surface of graphene oxide or graphene particles, not in the solvent, in the heterogeneous nucleation step. This is known by those skilled in the art as a liquid crystal template mechanism (GS Artard, Nature 378 (1995), pages 366-368). In this method, the sol precursor compound is converted into a sol and further a gel.

  Step (c) is usually carried out over a period of 0.5 hours to 2 days, preferably 1 to 24 hours, more preferably 2 to 8 hours. The temperature in step (c) is usually from 10 to 80 ° C., depending on the system, in particular depending on the solvent and / or dispersion used.

  Subsequently, the graphene oxide particles and the graphene particles exhibit a coating on both the top surface and the bottom surface by the specific gel. This gel is arranged according to the above-mentioned template formed on the surface of the particles by a marketed cationic surfactant and / or nonionic active agent. This provides a uniform and structured coating of the particle surface with the gel.

  Thereafter, the coated graphene oxide particles and graphene particles are subjected to further processing such as separation and drying.

  Following the step (c), the coated particles for removing the surfactant molecules by washing or heating from the coated graphene oxide particles or the coated graphene particles in the step (d) are washed with water, methanol, ethanol, Further, it may be washed with a solvent such as propanol. On the other hand, surfactant molecules may be removed by heating at 50 to 500 ° C. in an inert atmosphere. The surfactant particles may be removed during the heating of the graphene oxide particles in the step (e). Thereby, a graphene oxide can be converted into a graphene and process (d) and (e) can be performed together. Moreover, you may remove surfactant molecule | numerator by the baking process performed arbitrarily (it mentions later).

After removing and drying the coated particles, a firing step is optionally performed. In this firing step, the coated particles are fired at a high temperature in the presence of an oxygen-containing gas or an inert gas. In the case of particles coated with SiO ₂ , for example, firing is performed for 2 hours or more. The firing is preferably performed at 5 to 600 ° C. for 2 to 8 hours in an air atmosphere, for example.

  The coated catalyst usually contains 75-95 wt%, preferably 80-92 wt%, more preferably 85-90 wt% graphene oxide or graphene in the dry state, usually 5-25 wt%, Preferably 8-20% by weight, more preferably 10-15% by weight, of a coating formed from a gel is included.

  When step (a) prepares a mixture according to (a1), the coated graphene oxide particles are optionally heated to 500 ° C. or higher for at least 1 minute in an inert gas atmosphere. Thereby, graphene oxide can be reduced to graphene (step (e)). Preferably the coated graphene oxide particles are heated under an inert gas atmosphere for at least 30 minutes, more preferably for an hour or more. The heating is usually not performed for 12 hours or more, and preferably is not performed for 6 hours or more. The heating temperature is preferably in the range of 500 to 1000 ° C.

In an embodiment of the invention, the method comprises:
(A)
(A1) a mixture comprising graphene oxide particles, water, and one or more cationic surfactants and / or nonionic surfactants,
Preparing the process,
(B) adding one or more sol precursor compounds to the mixture obtained from step (a);
(C) reacting the mixture from step (b) by a sol / gel method to form a gel on graphene oxide particles or graphene particles;
(D) removing one or more surfactants; and (e) heating optionally coated graphene oxide particles to 500 ° C. or higher for 1 minute or longer in an inert gas atmosphere, Reducing to graphene,
Have
Particularly preferably, step (e) is actually performed.

In a particularly preferred embodiment, one or more sol precursor compounds are selected in step (b) from the SiO ₂ precursor compound, more preferably water glass and Si (OR) ₄ , and the above steps are performed. Here, R is, H, from _{CH 3, C 2 H 5,} C 2 H 4 OH, n-C 3 H 7, i-C 3 H 7, n-C 4 H 9, and t-C ₄ H ₉ It is selected and may be the same species or different species.

It is particularly preferred that SiO ₂ -coated 2-D sandwich nanomaterials based on graphene and / or graphene oxide according to the invention are used as templates for producing other 2-D sandwich nanomaterials. Accordingly, the present invention provides a method comprising the steps described above. In this method, the one or more sol precursor compounds in step (b) are selected from SiO ₂ precursor compounds. Furthermore, the method of the present invention includes the following steps.

(F) SiO ₂ coated graphene oxide particles or SiO ₂ coated graphene particles, metal oxide precursor, a metal precursor compound, and a carbon precursor at least one selected from compound precursor compounds include Process,
(G) a step of converting one or more precursor compounds into a corresponding metal oxide, a corresponding metal, or carbon, and (h) a step of removing SiO ₂ from the graphene oxide particles or graphene particles.

Therefore, the process according to the present embodiment is as follows.
(A)
(A1) Graphene oxide particles, water, and a mixture containing one or more cationic surfactants and / or nonionic surfactants, or (a2) one or more solvents useful for solution exfoliation of graphene particles and graphite And a mixture comprising one or more cationic surfactants and / or nonionic surfactants,
(B) adding one or more sol precursor compounds to the mixture from step (a);
(C) reacting the mixture from step (b) by a sol / gel method to form a gel on graphene oxide particles or graphene particles;
(D) removing one or more surfactants; and (e) heating optionally coated graphene oxide particles to 500 ° C. or higher for 1 minute or longer in an inert gas atmosphere, Reducing to graphene,
(F) SiO ₂ -coated graphene oxide particles or SiO ₂ -coated graphene particles are impregnated with one or more precursor compounds selected from a metal oxide precursor, a metal precursor compound, and a carbon precursor compound The process of
(G) converting one or more precursor compounds into corresponding metal oxides, corresponding metals, or carbon; and (h) removing SiO ₂ from the graphene oxide particles or graphene particles,
Including all.

Step (f), SiO ₂ coated graphene oxide particles or SiO ₂ coated graphene particles, one or more metal oxide precursor, one or more metal precursor compounds and / or one on the carbon precursor Including a body compound. Each precursor compound eventually fills the spaces / holes in the SiO ₂ coating that were originally filled with surfactant molecules.

  The one or more metal oxide precursor compounds and / or the one or more metal precursor compounds are preferably selected from metal halides, metal nitrates, metal alkoxides, metal sulfates, metal carbonates, and metal sulfates. Is done. The one or more carbon precursor compounds are selected from sucrose, glucose, and pitch.

The SiO ₂ coated particles are impregnated in a method of the kind in question using methods known by those skilled in the art. This method is, for example, a wet impregnation method. In this method, the porous material to be impregnated is suspended in a solution containing the corresponding precursor in excess and stirred several times, for example for 1 to 24 hours. The solution containing the above precursor in excess is then removed by filtration. Another suitable method is the initial wet impregnation method. In this method, the porous material to be impregnated is mixed with a solution of the corresponding precursor compound. The mixing is performed so that the amount of the precursor compound solution corresponds to the volume of the pores in the porous material. The suspension obtained in the above method is mixed mechanically.

  Useful solvents for metal and / or metal oxide precursor compounds and / or carbon precursor compounds include water and / or alcohols such as methanol, ethanol, and propanol. The density | concentration of the precursor compound in an impregnation solution is 10-30 mass% normally with respect to the total mass of an impregnation solution, Preferably it is the range of 15-25 mass%.

  Usually, the precursor compound has a mass ratio of precursor compound to uncoated particles of 0.1: 1 to 50: 1, preferably 0.5: 1 to 20: 1, more preferably 1: 1 to 10: Used to be 1.

  After impregnation, the particles are usually separated, optionally washed and dried.

  Step (g) includes treating the impregnated particles at a high temperature. This treatment can convert a particular precursor compound into the desired compound. The particles impregnated with the carbon precursor compound are usually heated to a temperature in the range of 600 to 900 ° C., preferably 650 to 800 ° C., more preferably 700 to 800 ° C. in an inert gas atmosphere. The heating time is 1 to 5 hours, preferably 2 to 4 hours. In order to convert the metal oxide precursor compound, the impregnated particles are usually heated to a temperature in the range of 200-500 ° C., preferably in the range of 300-400 ° C. in an oxygen-containing atmosphere (eg air). Heat. The heating time is usually 2 to 10 hours, preferably 4 to 8 hours. In order to convert the metal precursor, the impregnated and coated particles are usually heated to a temperature in the range of 200-600 ° C., preferably 300-500 ° C. in a reducing atmosphere (eg in the presence of hydrogen). The The heating time is usually 4 to 10 hours, preferably 5 to 8 hours.

  In step (h), the coated catalyst which removes silicon dioxide by dissolving in aqueous sodium hydroxide solution or HF or the like is repeatedly exchanged with, for example, aqueous sodium hydroxide solution in high concentration aqueous sodium hydroxide solution. However, you may stir at room temperature for 12 to 24 hours. The method described in steps (f) to (h) is basically known by those skilled in the art and is called nanocasting. A description of this method can be found, for example, in “A. Rumplecker et al., Chem. Mater. 19 (2007), page 485”.

In one embodiment of the present invention, the above steps (f), (g), and (h) are independently repeated one or more times alone or together with others. For example, the impregnation step may be repeatedly performed to impregnate the coated particles with a large amount of the precursor compound. Similarly, the conversion of one or more precursor compounds may be repeated so that very nearly complete conversion can be achieved. Similarly, the step (h) may be repeatedly executed continuously. In this case, the same type of solvent may be used repeatedly for the SiO ₂ solvent, or different types of solvents may be used.

  The coated particles usually contain 70 to 95% by weight, preferably 80 to 95% by weight, more preferably 85 to 90% by weight of graphene oxide or graphene in a dry state, and usually 5 to 30% by weight, preferably 5 to 20% by weight, more preferably 10 to 15% by weight, of a coating selected from carbon, metals and / or metal oxides.

  Moreover, this invention prepares the two-dimensional sandwich nanomaterial obtained by the above-mentioned method.

Furthermore, the present invention provides a method of using the sandwich nanomaterial obtained by the above-described method as a template for producing other nanomaterials. This method of use arises from the principle described above, which is called nanocasting by those skilled in the art. In nanocasting, “male” and “female” in the structure formed by the self-aggregating surfactant molecules of step (a) are produced in each case. Accordingly, in step (c), SiO ₂ forms a coating, the next surfactant molecule is removed, and the gap / hole portion originally filled with the surfactant molecule is filled with the carbon precursor compound or the like. The Next, the carbon precursor compound is converted to carbon having a three-dimensional structure originally formed by the surfactant molecules. The SiO ₂ is then removed to leave a carbon microstructure. The carbon fine structure is similarly impregnated again with a precursor compound such as a metal oxide precursor compound, and the carbon is removed by heating in an oxygen-containing atmosphere, so that the metal having the original SiO ₂ layer structure is obtained. An oxide layer is left.

  Furthermore, the present invention provides a two-dimensional sandwich nanomaterial obtained by the above-described method, a catalyst, a sensor, a capacitor, a primary and secondary electrochemical cell, and a fuel each containing the two-dimensional sandwich nanomaterial obtained by the above-described method. Prepare a method for use with batteries.

The two-dimensional sandwich nanomaterial obtained by the above method may be used for the production of graphene particles. Similarly, this method for producing graphene particles can be performed in the above-described preferred embodiments including steps (a) to (e). In this case, in the step (b), the one or more sol precursor compounds are selected from SiO ₂ precursor compounds. When step (a) prepares the mixture of (a1), step (e) is performed to convert the graphene oxide particles to graphene particles. Then, after step (e), step (f) (removal of SiO ₂ from graphene oxide particles) is performed. In particular, embodiments of the present invention
(A)
(A1) Graphene oxide particles, water, and a mixture containing one or more cationic surfactants and / or nonionic surfactants, or (a2) one or more solvents useful for solution exfoliation of graphene particles and graphite And a mixture comprising one or more cationic surfactants and / or nonionic surfactants,
Preparing the process,
(B) adding one or more sol precursor compounds to the mixture from step (a);
(C) reacting the mixture from step (b) by a sol / gel method to form a gel on graphene oxide particles or graphene particles;
(D) removing one or more surfactants; and (e) heating optionally coated graphene oxide particles to 500 ° C. or higher for 1 minute or longer in an inert gas atmosphere, Reducing to graphene; and (g) removing SiO ₂ .
including.

Here, it is particularly preferable to produce graphene particles from graphene oxide. The corresponding method is
(A)
(A1) a mixture comprising graphene oxide particles, water, and one or more cationic surfactants and / or nonionic surfactants,
(B) adding one or more sol precursor compounds to the mixture from step (a);
(C) reacting the mixture from step (b) by a sol / gel method to form a gel on graphene oxide particles or graphene particles;
(D) removing one or more surfactants; and (e) heating optionally coated graphene oxide particles to 500 ° C. or higher for 1 minute or longer in an inert gas atmosphere, Reducing to graphene; and (f) removing SiO ₂ .
including.

  The present invention also includes a method of using the two-dimensional sandwich nanomaterial obtained by the above-described method for producing graphene particles.

  The embodiments of the present invention will be described in more detail by way of examples.

Example 1: Production of SiO ₂ -coated graphene oxide particles by the Hummer method (Hummers, WS & Offman, RE; J. Am. Chem. Soc. 80 (1958), pages 1339 to 1139) Graphene oxide was produced from graphite flakes. First, 30 mg of the synthesized graphite oxide was suspended in an aqueous solution containing 1 g of cetyltrimethylammonium bromide and 40 mg of NaOH in 500 ml of demineralized water, and this was sonicated for 3 hours. Subsequently, the suspension was stirred for 2 hours at 40 ° C. using a magnetic stir bar, and 1 ml of tetraethyl orthosilicate (TEOS) was slowly added to this suspension. The resulting mixture was reacted for 12 hours, and then the SiO ₂ -coated graphene oxide particles were washed with heated ethanol, and separated and dried at 80 ° C. for 6 hours.

  Electron microscopy by field emission electron microscopy and transmission electron microscopy revealed that the particles have a size of 200 nm to several μm and a 2 nm sized mesoporous structure. No free silica particles or uncoated graphene oxide particles were found. This, as expected, is a surfactant molecule. This indicates that the graphene oxide particles are adsorbed on the surface of the graphene oxide particles by electrostatic interaction, and the heterogeneous nucleation of tetraethyl orthosilicate on the surface of the graphene oxide becomes uniform nucleation in the solution. The particle thickness in the direction perpendicular to the main plane of the planar particles was measured by analysis by atomic force microscopy. As a result of the measurement, the thickness was approximately 28 ± 1 nm.

Example 2: manufactured as of Example 1 SiO ₂ coated graphene particles from SiO ₂ coated graphene oxide particles, graphene oxide particles coated with the mesoporous SiO _2, under an argon atmosphere 800 Pyrolysis treatment was carried out at 3 ° C. for 3 hours. Thereby, since the particles are protected by the SiO ₂ coating, graphene oxide is efficiently reduced to graphene without agglomerating the particles. The morphology and structure of the SiO ₂ -coated graphene particles are stable during heat treatment and the mesoporous structure is not impaired during pyrolysis. This was shown by inspection with an electron microscope and a transmission electron microscope. When the graphene particles coated with SiO ₂ obtained in Example 2 were examined by the nitrogen adsorption method, it was found that the type IV of the nitrogen adsorption isotherm, which is a characteristic of uniform mesoporous, was exhibited. The pore size distribution was calculated to be 2 nm according to the Barrett-Joyner-Halenda method. The adsorption data showed a very high specific surface area of 980 m ² g ⁻¹ . The value of the specific surface area is considerably larger than that of mesoporous silicon dioxide produced conventionally.

Example 3 Production of Graphene Particles Coated with Mesoporous Carbon The SiO ₂ -coated graphene particles of Example 2 were repeatedly impregnated with an ethanol sucrose solution. Impregnation was performed by stirring at 40 ° C. In the final product by impregnation, the ratio of sucrose to SiO ₂ -coated graphene particles was fixed at 2: 1. Next, the sucrose-containing particles were dried and thermally decomposed at 700 ° C. for 3 hours in an argon atmosphere. Next, SiO ₂ was removed from the obtained particles in an aqueous NaOH solution to obtain graphene particles coated with mesoporous carbon.

Inspection of the carbon-coated particles by field emission electron microscopy revealed that the carbon layer had the same size as the SiO ₂ -coated graphene particles used as the template and a highly monodisperse structure. X-ray examination revealed that the carbon in the coating was present in the structure in an amorphous form. By examining the adsorption and desorption by the nitrogen adsorption method, it was found that a specific surface area of 910 m ² g ⁻¹ (according to Brunauer-Emmett-Teller equation) was exhibited. The particles exhibit a type IV isotherm, thus suggesting the presence of numerous mesoporous and microporous materials in the carbon-coated graphene particles.

Example 4: Production of graphene particles coated with Co ₃ O _{4 The} graphene particles coated with SiO _{2 in} Example 2 were repeatedly impregnated with a cobalt nitrate solution of ethanol. Impregnation was performed by stirring at 40 ° C. In the impregnation, the ratio of cobalt nitrate to SiO ₂ -coated graphene particles was 2.3: 1. The particles impregnated with cobalt nitrate were heated in air at 350 ° C. for 5 hours. The SiO ₂ was then removed from the resulting particles in an aqueous NaOH solution. Graphene particles coated with mesoporous carbon were obtained. High resolution transmission electron microscope revealed that Co ₃ O ₄ had a mesoporous structure but a crystal structure.

Example 5: Use of carbon-coated graphene particles in a lithium ion secondary battery An electrochemical test was performed on 2032 button cells. The carbon-coated graphene particles of Example 3, carbon black (Super-P), and poly (vinyl difluoride) (PVDF) were mixed at a mass ratio of 80:10:10, and the mixture was mixed with copper foil (99.99). The working electrode was manufactured by brushing to 6%, manufactured by Goodfellow. Lithium foil was used as the counter electrode. The electrolyte consists of a unipolar solution of LiPF ₆ in ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio 1: 1, industries Ltd). The battery was assembled in a groove box filled with argon. In the groove box, the water and oxygen concentrations were both less than 1 ppm. Electrochemical output was measured at various charge / discharge rates in the voltage range of 0.01 to 3.00V. The results are shown in Tables 1 and 2.

Claims (19)

A method for producing a two-dimensional sandwich nanomaterial,
(A)
(A1) a mixture comprising graphene oxide particles, water, and one or more cationic surfactants, or (a2) one or more solvents useful for exfoliating graphene particles, graphite, and one or more cationic interfaces Providing a mixture comprising an active agent;
(B) adding one or more sol precursor compounds to the mixture obtained from step (a);
(C) the step of reacting the mixture obtained from step (b) in a sol / gel method to form a gel from one or more sol precursor compounds to graphene oxide particles or graphene particles,
(D) removing the one or more surfactants, and (e) optionally heating the gel-coated graphene oxide particles to 500 ° C. or higher for 1 minute or longer in an inert gas atmosphere, Reducing graphene oxide to graphene,
Have
Of the two-dimensional sandwich nanomaterial characterized in that the nanomaterial exhibits an extension in the third direction in the range of 0.3 nm to 500 nm, this range also including this coating, if present Production method.   The process according to claim 1, wherein the cationic surfactant is selected from the group of quaternary ammonium compounds. One or more sol precursor compounds,
SiO ₂ precursor compound, ZrO ₂ precursor compound, TiO ₂ precursor compound, CeO ₂ precursor compound, Fe ₂ O ₃ precursor compound, MgO precursor compound, Al ₂ O ₃ precursor compound, Fe ₂ O ₃ precursor Body compound, Fe ₃ O ₄ precursor compound, MgO precursor compound, ZnO precursor compound, chromium oxide precursor compound, Co ₂ O ₃ precursor compound, molybdenum oxide precursor compound, tungsten oxide precursor compound The method according to claim 1 or 2, selected from the group consisting of: a precursor compound of hafnium oxide, a precursor compound of Y ₂ O ₃ , and a water-soluble crosslinked polymer and a polymer precursor. One or more sol precursor compounds,
Selected from the group consisting of metal halides, metal nitrates, metal carbonates, metal oxosulfates, metal acetylacetonates and metal alkoxides, and water glass for Si;
4. The method according to claim 1, wherein the metal is selected from the group consisting of Zn, Mg, Al, Y, Fe, Cr, Co, Si, Zr, Ti, Ce, Mo, W, and Hf. The manufacturing method as described. The production method according to claim 1, wherein the one or more sol precursor compounds are selected from SiO ₂ precursor compounds. One or more sol precursor compound, water glass, and is selected from Si (OR) ₄ (where the Si (OR) _4, R _{is, H, CH 3, C 2} H 5, C 2 H 4 OH N-C ₃ H ₇ , i-C ₃ H ₇ , n-C ₄ H ₉ , and t-C ₄ H ₉ , which may be the same or different). The production method according to claim 1. (F) SiO ₂ -coated graphene oxide particles or SiO ₂ -coated graphene particles are impregnated with one or more precursor compounds selected from a metal oxide precursor, a metal precursor compound, and a carbon precursor compound The process of
(G) a step of converting one or more precursor compounds into a corresponding metal oxide, a corresponding metal, or carbon, respectively, and (h) a step of removing SiO ₂ from the graphene oxide particles or the graphene particles, respectively. The manufacturing method of Claim 5 or 6.   The production method according to claim 7, wherein the steps (f), (g), and (h) are independently or independently repeated together with one or more times.   The metal oxide precursor compound and the metal precursor compound in step (f) are selected from the group consisting of metal halides, metal nitrates, metal alkoxides, metal sulfates, metal carbonates, and metal oxosulfates. Item 9. The manufacturing method according to Item 7 or 8.   The production method according to claim 7 or 8, wherein the carbon precursor compound in the step (f) is selected from the group consisting of sucrose, glucose, and pitch. Conversion of one or more precursor compounds in step (g),
The manufacturing method of any one of Claims 7-10 performed by heating the impregnated graphene oxide particle or a graphene particle, respectively. In step (h), the production method according to any one of claims 7-11 for removing SiO ₂ by dissolving aqueous sodium hydroxide solution or HF. A two-dimensional sandwich nanomaterial obtained by the method of claims 1-12,
The two-dimensional sandwich nanomaterial characterized in that the nanomaterial exhibits an extension in the third direction in the range of 0.3 nm to 500 nm, which range also includes this coating, if present.   14. The two-dimensional sandwich nanomaterial according to claim 13, wherein the nanomaterial is coated on the top and opposite surfaces of a sandwich-type layer structure having a coating / graphene or graphene oxide / coating arrangement.   The method of using the two-dimensional sandwich nanomaterial of any one of Claim 13 or 14 as a template for manufacture of another nanolayer material.   A method of using the two-dimensional sandwich nanomaterial according to claim 13 or 14 for a catalyst, a sensor, a capacitor, a primary and secondary electrochemical cell, and a fuel cell.   A catalyst, sensor, capacitor, primary and secondary electrochemical cell, and fuel cell comprising the two-dimensional sandwich nanomaterial according to claim 13 or 14.   A method of using the two-dimensional sandwich nanomaterial according to claim 13 or 14 for producing graphene particles. The steps (a) to (e) according to claim 5 or 6, and (h) a step of removing SiO ₂ from the graphene particles,
The manufacturing method of the graphene particle which performs a process (e), when the mixture of (a1) is prepared at the process (a).