JP7432306B2 - Method for manufacturing carbon material composite - Google Patents

Description

The present invention relates to a method for manufacturing a carbon material composite. More specifically, catalysts, electrode active materials for batteries and capacitors, thermoelectric conversion materials, conductive materials, luminescent materials, additives for lubricating oils, additives for polymers (resins), permeable membrane materials, antibacterial materials, and water-repellent materials. , relates to a method for producing a carbon material composite that can be suitably used as an adsorption material, etc.

Carbon materials have excellent properties such as hardness, and are used in various fields such as semiconductors, batteries, automobiles, information and communications, and industrial equipment.
Graphite oxide, a type of carbon material, is made by oxidizing graphite, which has a layered structure in which carbon atoms bonded with ^sp2 bonds are arranged in a plane, and adding oxygen-containing functional groups. Many studies have been conducted on its physical properties. Graphite oxide is used as catalysts, electrode active materials for batteries and capacitors, thermoelectric conversion materials, conductive materials, luminescent materials, additives for lubricating oils, additives for polymers, permeable membrane materials, antibacterial materials, water repellent materials, and adsorption materials. It is expected that it will be used for various purposes such as.

A common method for producing graphite oxide is to synthesize graphite oxide by reacting graphite with a strong oxidizing agent in an acid solvent, and the Hummers method using sulfuric acid and potassium permanganate as the oxidizing agent is well known. (See Non-Patent Document 1). Other known methods include the Brodie method using nitric acid and potassium chlorate, and the Staudenmaier method using sulfuric acid, nitric acid and potassium chlorate as oxidizing agents.

For example, in a method for producing an oxidized graphite derivative, between the step of oxidizing graphite and the step of obtaining the oxidized graphite derivative, a reaction solution containing graphite oxide obtained in the oxidation step has a solubility in water of 0.01% or more. It is disclosed that a graphite oxide-containing composition is separated after adding a solvent that is optionally immiscible with water (see Patent Document 1).
Incidentally, an aggregate formed by aggregating a complex obtained from purified graphene oxide (graphite oxide) and a cationic lipid has been disclosed (see Patent Document 2). In addition, in order to obtain a graphite oxide dispersion in which graphite oxide is well dispersed, low molecular weight polyethylene glycol was added to a dispersion of purified and dried graphite oxide powder dispersed in deionized water, and the mixture was treated with ultrasonic waves. This has been disclosed (see Non-Patent Document 2).

International Publication No. 2017/082263 Japanese Patent Application Publication No. 2012-153590

William S. Hummers, et.al, J. Am. Chem. Soc, 1958, 80, 1339. Vineet Dua, et.al, Angew. Chem. Int. Ed. 2010, 49, 1-5

As mentioned above, various methods are known for producing graphite oxide, which is a type of carbon material, but it is common to obtain graphite oxide through an oxidation process and then purify the graphite oxide from the reaction solution. Usually, centrifugation is repeated or the reaction solution is filtered. In the former case, there were problems in that the process became complicated and the amount of waste liquid increased, and in the latter case, there was a problem in that the filter was easily clogged. In either case, refining takes time and effort, leading to high costs, and there is room for improvement in terms of efficient production when producing graphite oxide. In particular, in Patent Document 2, it is assumed that a cationic lipid is reacted on purified graphite oxide to obtain a complex, and purification is required to produce the complex, which is expensive if carried out industrially. becomes. In contrast, the method described in Patent Document 1 makes it possible to efficiently separate graphite oxide through liquid/liquid separation of the aqueous layer and organic layer, making it possible to easily obtain high-quality graphite oxide. It is possible. On the other hand, in the industrial production of graphite oxide, there has been a strong desire to perform the separation process of graphite oxide, particularly the filtration process, more efficiently and to more easily produce high-quality graphite oxide.

The present invention has been made in view of the above-mentioned current situation, and an object of the present invention is to provide a method that can easily produce high-quality graphite oxide.

The present inventors have studied various ways to more easily produce high-quality graphite oxide, and have developed methods for purifying graphite oxide from an aqueous dispersion in which graphite oxide obtained in an oxidation process is dispersed. When an aqueous dispersion and a nonionic surfactant are mixed and then a carbon material composite containing the nonionic surfactant and graphite oxide is purified, acid remains in the aqueous dispersion. The carbon material composite aggregates due to the action of the nonionic surfactant even if it is mixed, forming large aggregates with low dispersibility, making it difficult for purification to occur, such as filter clogging even when filtering an aqueous dispersion. It has been found that the time required is extremely short, the acid can be sufficiently removed, and the carbon material composite can be purified extremely efficiently. The reason for this is thought to be as follows, according to the latest findings of the present inventors. First, regarding the effect of a carbon material composite coagulating due to the action of a nonionic surfactant even if acid remains, graphite oxide is a weak acid whose acid groups ionize in water, but in the presence of strong acids such as sulfuric acid, graphite oxide is a weak acid whose acid groups ionize in water. In this case, the acid group does not ionize and becomes neutral. Here, when an aqueous dispersion of graphite oxide obtained in the oxidation step is mixed with a nonionic surfactant, the graphite oxide and the nonionic surfactant interact hydrophobically, resulting in a nonionic It can be aggregated as a carbon material composite comprising a surfactant and graphite oxide. Further, since the carbon material composite is not strongly aggregated by the nonionic surfactant having a weak cohesive force, water enters the aggregate and can wash away the sulfuric acid. Furthermore, since the aggregation is not very strong, it is possible to easily break the aggregation through a peeling process and disperse it in the dispersion medium again. The present inventors have discovered that this purification method makes it possible to easily produce high-quality carbon material composites at low cost, and that this method is especially useful when applied to industrial production of carbon material composites. We have found that this effect is remarkable, and have come up with the idea that the above problems can be successfully solved, resulting in the present invention.

That is, the present invention is a method for producing a carbon material composite comprising a nonionic surfactant and oxidized graphite, which includes a step of oxidizing graphite, and a step of oxidizing graphite, and a step of oxidizing graphite. This method of producing a carbon material composite includes the step of mixing an aqueous dispersion of graphite oxide dispersed therein with a nonionic surfactant, and then refining the carbon material composite.

The present invention also provides a method for producing oxidized graphite, which includes a step of oxidizing graphite, and an aqueous dispersion in which the oxidized graphite obtained in the oxidation step is dispersed, and a nonionic interface. It is also a method for producing graphite oxide, which includes a step of refining graphite oxide after mixing with an activator.

In a preferred embodiment of the method for producing a carbon material composite of the present invention or the method for producing graphite oxide of the present invention, the purification step is performed using a method selected from the group consisting of filtration, decantation, centrifugation, and liquid separation extraction. This is a step of refining a carbon material composite or graphite oxide by at least one selected method.

By the method for producing a carbon material composite of the present invention, a high quality carbon material composite can be easily obtained at low cost. Moreover, the obtained carbon material composite can be dispersed very well in a dispersion medium.

The present invention will be explained in detail below.
In addition, a form in which two or more of the preferable features of the present invention described below in separate paragraphs are combined is also a preferable form of the present invention.

<Method for manufacturing carbon material composite>
In the method for producing a carbon material composite of the present invention, the order of the steps after the oxidation step is not particularly limited, but if necessary, after performing the oxidation reaction termination (quenching) step described later, the mixing step, The above purification steps are performed in this order. Further, a graphite oxide refining step may be further performed as appropriate before the above mixing step. For example, after performing an oxidation reaction termination step as necessary, the graphite oxide refining step, the mixing step, the refining step (carbon Material composite purification step) may be performed in this order.

The carbon material composite obtained by the method for producing a carbon material composite of the present invention is configured to contain a nonionic surfactant and graphite oxide.
The above-mentioned graphite oxide is a material in which oxygen is bonded by oxidizing a graphite carbon material such as graphene or graphite (oxygen is bonded to the carbon material). It exists as a substituent such as a carboxyl group, carbonyl group, hydroxyl group, or epoxy group.
The graphite oxide is preferably graphene oxide in which oxygen is bonded to carbon of graphene.
Note that graphene generally refers to a sheet consisting of a single layer in which carbon atoms bonded by sp ² bonds are arranged in a plane, and a stack of many graphene sheets is called graphite, but graphene oxide in the present invention This includes not only sheets consisting of only one layer of carbon atoms, but also sheets having a laminated structure of about 2 to 100 layers. It is preferable that the graphene oxide is a sheet consisting of only one layer of carbon atoms, or has a laminated structure of about 2 to 20 layers.
The graphite oxide may further have a functional group such as a sulfur-containing group or a nitrogen-containing group, but the content of carbon, hydrogen, and oxygen as constituent elements of all constituent elements is 97 mol% or more. It is preferable that the content is 99 mol % or more, and it is even more preferable that the graphite oxide contains only carbon, hydrogen, and oxygen as constituent elements.

In the following, first, regarding the purification step in the method for producing a carbon material composite of the present invention, the mixing of an aqueous dispersion in which graphite oxide obtained in the oxidation step is dispersed with a nonionic surfactant, and the carbon material The purification of the complex will be explained in order. Next, a process of peeling off the layers of graphite oxide contained in the carbon material composite purified in the purification process and a process of oxidizing the graphite before the purification process will be described.

(purification process)
[Mixing of aqueous dispersion and nonionic surfactant]
In the present invention, an aqueous dispersion in which graphite oxide obtained in the oxidation step is dispersed and a nonionic surfactant are mixed.
The mixing method is not particularly limited and can be carried out appropriately by any known method, but for example, the solid content may be uniformly dispersed by stirring, ultrasonication, or by using a known dispersion machine. is preferred.
When mixing the aqueous dispersion and the nonionic surfactant, for example, the nonionic surfactant may be added to the aqueous dispersion, or the aqueous dispersion may be added to the nonionic surfactant. Alternatively, the aqueous dispersion and the nonionic surfactant may be added to the reaction vessel at the same time.

In this specification, the nonionic surfactant is a compound having a hydrophobic group and a hydrophilic group, which is generally called a surfactant, and is an aqueous system in which graphite oxide obtained in an oxidation process is dispersed. It does not substantially ionize into ions in the dispersion.
Graphite oxide interacts hydrophobically with such a nonionic surfactant and aggregates as a carbon material composite. Thereby, purification steps such as filtration can be performed efficiently, and the manufacturing cost of the carbon material composite can be reduced.

Preferred examples of the hydrophobic group of the nonionic surfactant include hydrocarbon groups such as aliphatic hydrocarbon groups and aromatic hydrocarbon groups. The number of carbon atoms in the hydrocarbon group is more preferably 3 or more, even more preferably 6 or more, and particularly preferably 9 or more. The number of carbon atoms in the hydrocarbon group is preferably 24 or less, for example. Further, as the hydrophilic group of the nonionic surfactant, for example, an alkylene oxide group, an ether group, an ester group, an amide group, a hydroxyl group, etc. are mentioned as preferable ones. More preferably, the alkylene oxide group is an ethylene oxide group.
Examples of the nonionic surfactants include polyoxyethylene alkyl ether, polyoxyethylene alkenyl ether, polyoxyethylene alkylphenyl ether, higher fatty acid alkanolamide or its ethylene oxide adduct, sucrose fatty acid ester, alkyl glycooxide. Preferred examples include fatty acid glycerin monoester, alcohol ethoxylate, sorbitan esters, polyoxyethylene sorbitan esters, and derivatives thereof, and one or more of these may be used. For example, nonionic surfactants include those that have a hydroxyl group (-OH) at the end of the (poly)ethylene glycol chain of alcohol ethoxylate (for example, Softanol 50, Softanol 120 [manufactured by Nippon Shokubai Co., Ltd.]), Particularly preferred are oxyethylene sorbitan esters (eg, Nucol 85 [manufactured by Nippon Nyukazai Co., Ltd.]).

The amount of nonionic surfactant mixed with the aqueous dispersion in the above purification step may be set appropriately, but it is 10 to 1000 mass% based on 100 mass% of graphite oxide in the aqueous dispersion in which graphite oxide is dispersed. % is preferable. The amount of the nonionic surfactant is more preferably 20 to 700% by mass, and even more preferably 30 to 600% by mass, based on 100% by mass of graphite oxide in the aqueous dispersion containing graphite oxide. Particularly preferred is 40 to 500% by mass.

The above aqueous dispersion may be a reaction composition immediately after the oxidation step, and sulfuric acid may be removed from the reaction composition in the subsequent concentration step, or water and/or Although the solution may be one in which aqueous hydrogen peroxide is added, for example, a solution in which water and/or aqueous hydrogen peroxide are added to the reaction composition in the oxidation reaction termination step is preferable.
Note that the aqueous dispersion only needs to contain water as a dispersion medium, and may further contain an organic dispersion medium that is miscible with water, but from the viewpoint of ease of agglomeration of the carbon material composite, , it is preferable not to contain an organic dispersion medium.

In the method for producing a carbon material composite of the present invention, the aqueous dispersion (aqueous dispersion before mixing with the nonionic surfactant) has a water concentration of 20% by mass or more based on 100% by mass of the aqueous dispersion. It is preferable that
The water concentration is more preferably 25% by mass or more, even more preferably 30% by mass or more, and particularly preferably 35% by mass or more.
By keeping the water concentration within this range, even in the presence of sulfuric acid used in the oxidation process, the unexpected action of the nonionic surfactant interacting with graphite oxide and coagulating is more effective. The effect of the present invention becomes more pronounced.
Further, the water concentration is preferably 99% by mass or less, and more preferably 95% by mass or less, for example.

In the method for producing a carbon material composite of the present invention, the aqueous dispersion mixed with the nonionic surfactant preferably contains 1% by mass or more of sulfate ions based on 100% by mass of the aqueous dispersion.
The content of the sulfate ions is more preferably 3% by mass or more, and even more preferably 5% by mass or more. Further, the content of the sulfate ions is preferably 90% by mass or less, more preferably 70% by mass or less.
The content of sulfate ions is the total content of sulfate ions derived from sulfuric acid and sulfate ions derived from sulfate.
Furthermore, the pH of the aqueous dispersion is preferably 2 or less, more preferably 1.5 or less. The lower limit of pH is not particularly limited, but is usually -1 or higher.
In the present invention, in the presence of a strong acid such as sulfuric acid used in the oxidation step, the nonionic surfactant interacts with graphite oxide and aggregates, which is an unexpected effect, and the effects of the present invention can be exhibited.

[Refining process of carbon material composite]
After mixing the aqueous dispersion in which graphite oxide obtained in the oxidation step is dispersed and a nonionic surfactant, a step of refining the carbon material composite is performed. Note that the purification step is not particularly limited, and conventionally known methods can be used as appropriate. It is preferable that the process is a step of:
By using these methods, sulfuric acid in the aqueous dispersion can be efficiently and sufficiently removed, and the carbon material composite can be purified in a short time. As a result, during the purification of the carbon material composite, it is possible to sufficiently prevent the reactive oxygen-containing functional groups of the graphite oxide contained in the carbon material composite from being reduced and/or inactivated, resulting in a high quality product. A carbon material composite can be obtained. In this specification, the purification process refers to the process of removing solid impurities (for example, oxidizing agents such as permanganate) and/or solvents during oxidation reactions (strong acids such as sulfuric acid, etc.) from the aqueous dispersion. To tell.
Among these methods, filtration and separation/extraction are more preferred, and filtration is still more preferred. According to the above purification process, the action of the nonionic surfactant promotes the aggregation of the carbon material composite particles in the aqueous dispersion, and the carbon material composite particles become large aggregates, and as a result, the aqueous dispersion Filter clogging is unlikely to occur during filtration, and the time required for filtration is extremely short. Furthermore, since the carbon material composite is not strongly aggregated by the nonionic surfactant having a weak cohesive force, water enters the aggregate and the sulfuric acid can be sufficiently washed away. Therefore, by using filtration as a method for purifying a carbon material composite, a high quality carbon material composite can be obtained very easily.

In the method for producing a carbon material composite of the present invention, from the viewpoint of obtaining the carbon material composite more easily, the purification step is preferably performed by two or less of the above methods, and one method is preferred. More preferably, it is carried out by. Furthermore, it is one of the preferred embodiments of the manufacturing method of the present invention that the above method is completed in one step without repeating it.
Furthermore, from the viewpoint of more fully refining the carbon material composite, it is preferable to repeat the above method. Among these, one preferred form of the production method of the present invention is to repeatedly perform at least one method selected from the group consisting of filtration, decantation, centrifugation, and liquid separation extraction.
The purification step may be performed in air or in an atmosphere of an inert gas such as nitrogen, helium, or argon. Moreover, it may be carried out under any of pressurized conditions, normal pressure conditions, and reduced pressure conditions.

The production method of the present invention includes, for example, purifying the carbon material composite by at least one method selected from the group consisting of filtration, decantation, centrifugation, and liquid separation extraction, and then performing other purification such as washing with water. It may include a process. In addition, when washing with water is repeated after the above purification step, the number of washings is, for example, once, from the viewpoint of removing sulfuric acid more fully and peeling off the graphite oxide layer more appropriately in the peeling step described later. The number of times is preferably at least 1, and more preferably 2 or more times. In addition, from the viewpoint of not removing too much nonionic surfactant from the carbon material composite obtained by the production method of the present invention, the number of washings with water is preferably 10 times or less, and 7 times or less. is more preferable. Note that from the viewpoint of not removing too much of the nonionic surfactant, a mixed solution of water and a nonionic surfactant may be used instead of water for washing. Further, by preparing this cleaning liquid, it is also possible to arbitrarily adjust the ratio of graphite oxide to nonionic surfactant in the carbon material composite finally obtained.

(Peeling process)
Moreover, it is preferable that the manufacturing method of the present invention further includes a step of peeling off the layers of graphite oxide contained in the carbon material composite purified in the above-mentioned refining step. As mentioned above, the peeling process is a process of peeling off the layers of graphite oxide, and can be performed by ultrasonic treatment, homogenizer treatment, etc., and usually the carbon material composite containing graphite oxide from which the layers have been peeled off in the peeling process. The body is dispersed in a dispersion medium. The peeling step can be performed after mixing a dispersion medium with a carbon material composite comprising a nonionic surfactant and graphite oxide purified in the purification step. The dispersion medium may be either an aqueous dispersion medium containing water or an organic dispersion medium, including carbonate esters such as ethylene carbonate and propylene carbonate, lactams such as N-methyl-1-pyrrolidone, dimethylformamide, dimethyl Amides such as acetamide, ethers such as tetrahydrofuran and diethyl ether, lactones such as γ-butyrolactone, alcohols such as methanol, ethanol, propanol, and diacetone alcohol, ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, and acetic acid. Esters such as methyl, ethyl acetate, and butyl acetate, water, and the like are preferred, and one or a mixture of two or more of these can be used as a dispersion medium. Among these, carbonate esters, lactams, amides, ethers, lactones, alcohols, and water are more preferred, and propylene carbonate, N-methyl-1-pyrrolidone, dimethylformamide, dimethylacetamide, tetrahydrofuran, γ-butyrolactone, and Acetone alcohol and water are more preferred, and γ-butyrolactone, diacetone alcohol and water are particularly preferred. In other words, an aqueous dispersion medium is preferred.
The above purification process can sufficiently remove sulfuric acid, and the action of the nonionic surfactant on graphite oxide is moderate and not too strong, so the graphite oxide layer can be peeled off very well in the peeling process. As a result, the carbon material composite can be dispersed in the dispersion medium.

Further, as the dispersion medium, a liquid polymer compound is also preferable. Examples of the liquid polymer compound include polyethylene glycol, polypropylene glycol, silicone oil, etc., and one or more of these can be used.

Furthermore, as the dispersion medium, a resin precursor (monomer) is also preferable. The resin precursor may be a hydrophilic (aqueous) resin precursor or a lipophilic (organic) resin precursor, and may include conventionally known thermoplastic resin precursors and thermosetting resin precursors. , a precursor of a photocurable resin, etc. can be used as appropriate.

Examples of the thermoplastic resin include olefin resins such as polyethylene, polypropylene, ethylene-olefin copolymers (ethylene-propylene copolymers, etc.), polymethylpentene; poly(meth)acrylate resins, poly(meth)acrylic Acid resin, (meth)acrylic resin such as poly(meth)acrylonitrile resin; polystyrene, AS resin (acrylonitrile-styrene resin), ABS resin (acrylonitrile-butadiene-styrene resin), ACS resin (chlorinated polyethylene-acrylonitrile-styrene resin) styrenic resins such as AES resins (acrylonitrile-ethylene-styrene resins); halogenated vinyl resins such as polyvinyl chloride, polyvinylidene chloride, and polyvinylidene fluoride; amide resins such as aliphatic polyamides and aromatic polyamides; Vinyl acetate resins such as vinyl acetate and ethylene-vinyl acetate copolymers; other vinyl resins such as polyvinyl alcohol resins, polyvinyl acetal resins, polyvinyl ether resins, and polyvinyl ketone resins; polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc. Polyester resin; PPE resin (polyphenylene ether resin), modified PPE resin, polyphenylene oxide, polyphenylene sulfide, and other phenylene group-containing resins; polytetrafluoroethylene and other fluororesins; polyetheretherketone, polyetherketone, polyethersulfone, polyester resin; Polyether resins such as ether nitrile; polycarbonates; silicone resins; polysulfone resins; liquid crystal polymers; and copolymers obtained by appropriately combining monomers used to obtain these resins.

Examples of the thermosetting resin include epoxy resin, phenol resin, cyanate ester resin, melamine resin, polyimide resin, bismaleimide resin, urea resin, alkyd resin, silicone resin, vinyl ester resin, benzoxazine resin, urethane resin, etc. can be mentioned.

Examples of the photocurable resin include photocurable (meth)acrylic resins such as urethane (meth)acrylic resins and epoxy (meth)acrylic resins; polyvinyl carbonate resins such as polyvinyl acetate resins, and the like.

As the resin precursor, monomers used to obtain the above-mentioned resins (e.g., thermoplastic resins, thermosetting resins, photocurable resins) can be used, and among them, monomers having an ethylenically unsaturated double bond can be used. (vinyl monomer) and epoxy compound (epoxy monomer) are preferred.
The monomer having an ethylenically unsaturated double bond may be monofunctional or polyfunctional, such as (meth)acrylic ester, (meth)acrylic acid, (meth)acrylonitrile, etc. (Meth)acrylic monomer: Examples include styrene monomers such as styrene and divinylbenzene, and other vinyl monomers such as vinyl acetate, vinyl chloride, vinyl ether, and butadiene, and one or more of these may be used.
Further, examples of the above-mentioned epoxy compounds include alicyclic epoxy compounds, aromatic epoxy compounds, hydrogenated epoxy compounds, etc., and one or more of these can be used.

Further, the dispersion medium may be a mixed dispersion medium that is a combination of at least two selected from the group consisting of water, an organic dispersion medium, a liquid polymer compound, and a resin precursor.
For example, the above-mentioned liquid polymer compound or resin precursor may be dissolved or dispersed in an aqueous dispersion medium or an organic dispersion medium.

Further, the dispersion medium may contain a resin. For example, the dispersion medium may contain water and/or an organic dispersion medium, and the above-mentioned resin may be dissolved or dissolved in the water and/or organic dispersion medium. It may be dispersed. Examples of the resin include the above-mentioned thermoplastic resins, thermosetting resins, and photocurable resins, and one or more of these can be used. For example, water in which a water-soluble resin is dissolved, emulsion particles dispersed in water, or organic dispersion medium in which a polymer such as a vinyl resin is dissolved can be suitably used as the dispersion medium.
Note that, as the organic dispersion medium, it is preferable to use an organic dispersion medium that is preferable in the above-mentioned peeling process.

To summarize the above, the dispersion medium may be one selected from the group consisting of water, an organic dispersion medium, a liquid polymer compound, a resin, and a resin precursor, or an appropriate combination of at least two of them. A mixed dispersion medium may be used.

As mentioned above, among the above dispersion media, examples of resin dispersion media containing resins and/or resin precursors include epoxy compounds (epoxy monomers), epoxy resins, and monomers having ethylenically unsaturated double bonds. (vinyl monomer), vinyl resin, a copolymer obtained by combining two or more of these monomers, and a mixed dispersion medium of two or more of these monomers are preferred. Further, the resin dispersion medium may further contain an organic dispersion medium and/or water.

In addition, it is preferable that the sulfuric acid content in the dispersion medium in the above peeling step is, for example, 0.1% by mass or less based on 100% by mass of the dispersion medium.

The above peeling step can be performed, for example, in air or in an inert gas atmosphere such as nitrogen, helium, or argon. Furthermore, the temperature conditions for the above-mentioned peeling step are not particularly limited, but it is preferably carried out within a range of, for example, 10 to 50°C. Further, the pressure conditions in the above-mentioned peeling step are not particularly limited, and may be carried out under any of pressurized conditions, normal pressure conditions, and reduced pressure conditions, but it is preferable to carry out, for example, under normal pressure conditions.
The time for the above-mentioned peeling step may be adjusted as appropriate depending on the total amount of the carbon material composite dispersion liquid and the size of the peeling device, and can be, for example, from 1 minute to 120 hours. Further, the time is preferably 1 to 100 minutes, and more preferably 2 to 80 minutes.

(Process of oxidizing graphite)
In the step of oxidizing graphite, the method is not particularly limited as long as graphite is oxidized, and any method of oxidizing graphite such as the Hummers method, Brodie method, Staudenmaier method, etc. described above may be used. It may also be a step of adding permanganate to a mixed solution containing graphite and sulfuric acid, which employs the oxidation method in the Hummers method.

In the method of oxidizing graphite described above, the oxidation step usually involves oxidizing graphite using an acid.
In the production method of the present invention, acid remains in the aqueous dispersion that is subjected to the purification process, but even if the acid remains, the nonionic surfactant interacts with graphite oxide and aggregates, An unexpected effect is that it becomes possible to easily remove impurities such as acids. As a result, a high quality carbon material composite can be easily manufactured.

Among these, it is one of the preferred embodiments of the present invention that the oxidation step is a step of adding permanganate to a mixed solution containing graphite and sulfuric acid.
In the oxidation step, the amount of sulfuric acid used is preferably such that the mass ratio of sulfuric acid to graphite (sulfuric acid/graphite) is 25 to 60. When the mass ratio is 25 or more, oxidized graphite can be efficiently produced by sufficiently preventing the reaction composition (mixture) from increasing in viscosity during the oxidation reaction. Further, by setting the mass ratio to 60 or less, the amount of waste liquid can be sufficiently reduced.

The graphite used in the oxidation step preferably has an average particle diameter of 3 μm or more and 80 μm or less. By using particles having such an average particle size, the oxidation reaction can proceed more efficiently. The average particle diameter of graphite is more preferably 3.2 μm or more and 70 μm or less.
As the average particle diameter, it is preferable to adopt a volume-based average particle diameter measured by a laser diffraction/scattering particle size distribution analyzer.

The shape of the graphite used in the oxidation step is not particularly limited, and examples thereof include fine powder, powder, granules, granules, scales, polyhedrons, rods, and shapes containing curved surfaces. Particles with an average particle size in the above range can be obtained by, for example, pulverizing the particles with a pulverizer, screening the particles with a sieve, or a combination of these methods. It is possible to produce particles by optimizing the preparation conditions at the step of obtaining particles with a desired particle size.

The content of graphite in the mixed liquid containing graphite and sulfuric acid is preferably 0.5% by mass or more, more preferably 1% by mass or more, based on 100% by mass of the mixed liquid.1. It is more preferably 5% by mass or more, and particularly preferably 2% by mass or more. The graphite content is preferably 10% by mass or less, more preferably 8% by mass or less, even more preferably 7% by mass or less, and particularly preferably 6% by mass or less.
Only one type of graphite may be used in the oxidation step in the production method of the present invention, or two or more types of graphite that differ in any of the above average particle diameters, shapes, etc. may be used.

When the above oxidation step is a step of adding permanganate to a mixed solution containing graphite and sulfuric acid, the permanganate added in the above oxidation step includes sodium permanganate, potassium permanganate, permanganate. Examples include ammonium acid, silver permanganate, zinc permanganate, magnesium permanganate, calcium permanganate, barium permanganate, etc., and one or more of these can be used, but among them, sodium permanganate , potassium permanganate is preferred, and potassium permanganate is more preferred.

When the oxidation step is a step of adding permanganate to a mixed solution containing graphite and sulfuric acid, the total amount of permanganate added in the oxidation step is 100% by mass of graphite in the mixed solution. It is preferably 50 to 500% by mass. Thereby, graphite oxide can be produced safely and efficiently. Note that by changing the total amount of the oxidizing agent added, the amount of oxygen atoms introduced into the oxidized graphite can be adjusted.

When the above oxidation step is a step of adding permanganate to a mixed solution containing graphite and sulfuric acid, in the above oxidation step, permanganate may be added all at once, or may be added in multiple steps. Although it may be added continuously or it may be added continuously, it is preferable to add it in multiple portions or to add it continuously. This makes it possible to prevent the oxidation reaction from progressing rapidly, making it easier to control the reaction.
When the permanganate is added in multiple portions, the amount added per time may be the same or different.

When the oxidation step is a step of adding permanganate to a mixed solution containing graphite and sulfuric acid, in the oxidation step, permanganate is added while maintaining the temperature of the mixed solution within a range of 10 to 50°C. Preferably, salt is added. By maintaining the temperature within this range, the oxidation reaction can be controlled and allowed to proceed sufficiently.
Further, when the oxidation step is a step of adding permanganate to a mixed solution containing graphite and sulfuric acid, the oxidation step adds permanganate while maintaining the temperature change of the mixed solution at 30°C or less. Preferably, it is a step of adding. Thereby, the oxidation process can be performed more stably.

When the above oxidation step is a step of adding permanganate to a mixed solution containing graphite and sulfuric acid, in the above oxidation step, from the viewpoint of performing the oxidation step stably, the permanganate is added for 10 minutes to 10 hours. It is preferable to add it over a period of time.

The above oxidation step is preferably performed while stirring using a known stirrer or the like.
The above oxidation step can be performed, for example, in air or in an inert gas atmosphere such as nitrogen, helium, or argon. Further, the pressure conditions of the oxidation step are not particularly limited, and may be performed under pressurized conditions, normal pressure conditions, or reduced pressure conditions, but it is preferable to carry out, for example, under normal pressure conditions.
The above oxidation step may be performed continuously or intermittently.

The above liquid mixture can be obtained by mixing graphite, sulfuric acid, and other components as necessary. The above-mentioned mixing can be carried out appropriately by a known method, but it is preferable to uniformly disperse graphite by, for example, performing ultrasonic treatment or using a known disperser.

The method for producing a carbon material composite of the present invention may include other steps such as an aging step, an oxidation reaction termination step, and a concentration step between the above-mentioned graphite oxidizing step and the above-mentioned purification step. . As mentioned above, for example, it is preferable to use a liquid obtained by adding water and/or hydrogen peroxide to the reaction composition in the oxidation reaction termination step as an aqueous dispersion in the purification step.

In the above aging step, the temperature and time for aging the reaction composition obtained in the oxidation step may be selected as appropriate, but it is preferable to maintain the reaction composition at a temperature of 0 to 90°C.
Further, the aging time is preferably 0.1 to 24 hours.

The oxidation reaction termination step may be performed in air or in an inert gas atmosphere such as nitrogen, helium, or argon. Alternatively, it may be carried out in a vacuum.
In the oxidation reaction termination step, for example, the temperature of the reaction composition is set at 5 to 15°C, water is added to the reaction composition, and then hydrogen peroxide solution is added as a reducing agent, or only hydrogen peroxide solution is added. This can be done by adding. Alternatively, the reaction composition may be added to water or hydrogen peroxide solution set at 5 to 25°C.
The time for the oxidation reaction termination step can be, for example, 0.01 to 5 hours.

By appropriately removing acid and water from the reaction composition through the above concentration step, the amount of acid and water can be adjusted within a suitable range. This step can be performed using methods such as centrifugation, redispersion by adding water, filtration, and concentration under reduced pressure. Further, although these steps may be repeated, it is preferable to complete them in one step without repeating them.

The production method of the present invention includes, after the above purification step, reacting graphite oxide contained in the carbon material composite purified in the purification step with a compound that reacts with an oxygen-containing functional group of graphite oxide to produce a graphite oxide derivative. It may include a step of obtaining.
The compound that reacts with the oxygen-containing functional group of the graphite oxide preferably contains at least one selected from the group consisting of, for example, alcohol, silane compound, fatty acid (salt), fatty acid ester, isocyanate compound, and amine. . Note that the silane compound preferably has a siloxy group and/or an alkoxy group directly bonded to a silicon atom, from the viewpoint of improving reactivity with the oxygen-containing functional group of graphite oxide.

<Carbon material composite>
The present invention is a carbon material composite comprising at least a nonionic surfactant and graphite oxide. The carbon material composite of the present invention can be suitably dispersed in a dispersion medium. A preferred form of the carbon material composite of the present invention is a carbon material composite comprising a nonionic surfactant and graphite oxide, wherein the graphite oxide has a ratio of the number of carbon atoms to the number of oxygen atoms ( A carbon material composite having a C/O) of 5.5 or less. This carbon material composite can be more fully dispersed in a dispersion medium.
The ratio is preferably 5 or less, more preferably 4 or less. Moreover, it is preferable that it is 1 or more.
The ratio of the number of carbon atoms to the number of oxygen atoms can be confirmed by the ratio of the total peak area in the O1s region and the total peak area in the C1s region obtained by XPS measurement.
The carbon material composite of the present invention can be obtained by the method for producing a carbon material composite of the present invention.

<Dispersion>
The present invention also provides a dispersion in which the carbon material composite of the present invention is dispersed in a dispersion medium.
The dispersion medium may be either an aqueous dispersion medium or an organic dispersion medium, and the above-mentioned water and organic dispersion medium can be suitably used in the stripping process. For example, propylene carbonate, N-methyl-1-pyrrolidone, dimethylformamide, etc. , dimethylacetamide, tetrahydrofuran, γ-butyrolactone, diacetone alcohol, water and the like are preferred, and γ-butyrolactone, diacetone alcohol and water are more preferred. Note that one type or a mixed dispersion medium of two or more of these dispersion media can be used.

In addition to water and an organic dispersion medium, the above-mentioned liquid polymer compound, resin, or resin precursor can be suitably used as the dispersion medium. As the liquid polymer compound, resin, and resin precursor, those shown in the description of the peeling process can be used, and the preferable ones are the same as those mentioned above in the description of the peeling process.
Suitable examples of the liquid polymer compound include polyethylene glycol and polypropylene glycol.
Suitable examples of the resin include vinyl resins such as (meth)acrylic resins and epoxy resins.
Suitable examples of the resin precursor include vinyl monomers such as (meth)acrylic monomers and epoxy monomers.
The dispersion medium may be a mixed dispersion medium in which at least two selected from the group consisting of water, an organic dispersion medium, a liquid polymer compound, a resin, and a resin precursor are appropriately combined. Preferred combinations are as described above in the stripping step.
Note that as the organic dispersion medium, it is preferable to use an organic dispersion medium that is preferable in the above-described peeling process.
The content ratio of the carbon material composite of the present invention in the dispersion of the present invention can be adjusted as appropriate.

As described above, the dispersion of the present invention may be one in which the carbon material composite of the present invention is dispersed in a resin and/or a resin precursor (resin dispersion). Note that the resin dispersion may further contain at least one selected from the group consisting of water, an organic dispersion medium, and a liquid polymer compound as a dispersion medium.

The resin dispersion may be in the form of a liquid or gel composition, or may be a solid (for example, a molded body).
The resin dispersion may be, for example, a dispersion obtained by dispersing the carbon material composite of the present invention in an aqueous dispersion medium or an organic dispersion medium, or the carbon material composite of the present invention itself (powder), and the above-mentioned carbon material composite. It can be obtained through a process of kneading (preferably kneading after melting the resin) a resin (thermoplastic resin, thermosetting resin, or photocurable resin).
Further, the above-mentioned molded body can be obtained, for example, by using the resin dispersion of the present invention, which is a liquid or gel composition; for example, by coating/forming the composition into a film, It can be obtained by molding or by polymerizing and curing a resin precursor in the composition.
Examples of the resin dispersion of the present invention include liquid or gel compositions; solid compositions such as films, sheets, fibers, pellets, and particles.
Examples of the film include a coating film, a self-supporting film, and the like.

<Production method of graphite oxide>
The present invention is a method for producing oxidized graphite, which includes a step of oxidizing graphite, an aqueous dispersion in which the oxidized graphite obtained in the oxidation step is dispersed, and a nonionic surfactant. It is also a method for producing graphite oxide, which includes a step of refining graphite oxide after mixing the graphite with an agent.
In a preferred embodiment of the method for producing graphite oxide of the present invention, the purification step is performed to obtain a carbon material composite by at least one method selected from the group consisting of filtration, decantation, centrifugation, and liquid separation extraction. This is the process of refining.
The method for producing graphite oxide of the present invention can be carried out by the same method as the method for producing the carbon material composite of the present invention described above. After that, graphite oxide can be obtained by removing impurities and the nonionic surfactant from the carbon material composite by repeatedly washing with water. Note that from the viewpoint of removing the nonionic surfactant, washing with water that does not contain the nonionic surfactant (the above-mentioned water washing) is preferable. The method for producing graphite oxide of the present invention allows high-quality graphite oxide to be easily obtained.
For example, the step of refining graphite oxide can be rephrased as a step of removing the surfactant so that substantially no nonionic surfactant remains.
The phrase "substantially no nonionic surfactant remains" means, for example, that the mass proportion of the nonionic surfactant is 1000 ppm or less.

Any of the carbon material composite obtained by the method for producing a carbon material composite of the present invention, the carbon material composite of the present invention, the dispersion of the present invention, and the graphite oxide obtained by the method for producing graphite oxide of the present invention, Suitable for use as electrode active materials for batteries and capacitors, thermoelectric conversion materials, conductive materials, luminescent materials, lubricating additives, polymer additives, permeable membrane materials, antibacterial materials, water repellent materials, adsorption materials, etc. Can be done.
Since the carbon material composite and graphite oxide obtained by the production method of the present invention are suitably dispersed in an aqueous dispersion medium, they can be particularly suitably used in applications where water or moisture may be present.
Note that examples of the above-mentioned batteries include lithium ion secondary batteries, solid polymer fuel cells, metal-air batteries, and the like.
Thermoelectric conversion devices using the above thermoelectric conversion materials include, for example, geothermal/hot spring thermal power generators, solar thermal power generators, waste heat generators for factories and automobiles, body temperature generators, etc. Examples include various electrical products, electric motors, artificial satellites, etc.

The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to these Examples. In addition, unless otherwise specified, "parts" shall mean "parts by mass" and "%" shall mean "% by mass."

<Synthesis of aqueous dispersion containing graphite oxide>
(Synthesis example)
Graphite oxide was synthesized using the following steps. 15 g of graphite (Z-25 manufactured by Ito Graphite Co., Ltd.) and 640 g of sulfuric acid (manufactured by Wako Pure Chemical Industries, Ltd.) were placed in a reaction vessel in advance, and potassium permanganate (manufactured by Wako Pure Chemical Industries, Ltd.) was added while adjusting the temperature to 30°C. 45g was added. After the addition, the temperature was raised to 35° C. for 30 minutes, and the reaction was allowed to proceed for 2 hours. After the reaction, 1070 ml of water and 42 ml of 30% hydrogen peroxide solution (manufactured by Wako Pure Chemical Industries, Ltd.) were added to the reaction solution to stop the reaction, and an aqueous dispersion containing graphite oxide (total mass of water 1812 g, concentration in terms of raw material graphite 0.83%) was added. , water concentration of 61%, and sulfate ion concentration of 36%). The C/O of graphite oxide in the obtained graphite oxide-containing aqueous dispersion was 1.8.

<Evaluation of purification efficiency>
(Example 1)
Softanol 120 (manufactured by Nippon Shokubai Co., Ltd.) was added in an amount of 0.75 mass equivalent to the raw material graphite to the aqueous dispersion containing oxidized graphite (100 g) obtained in the above synthesis example, and coagulated. After stirring, the mixture was filtered, and the filterability was very good (filtration was completed within 10 minutes). In addition, when water was poured into the filtered wet cake and then filtered and washed with water, good filterability was maintained (filtration was completed within 10 minutes). Water washing was performed twice, and good filterability was maintained both times.

(Example 2)
Same as Example 1 except that the same amount of Softanol 50 (manufactured by Nippon Shokubai Co., Ltd.) was used as a nonionic surfactant instead of 0.75 mass equivalent of Softanol 120 (manufactured by Nippon Shokubai Co., Ltd.) based on the raw material graphite. When the filtration performance was confirmed in the same manner as described above, the filtration performance was found to be good.

(Example 3)
Example 1 except that the same amount of Nucol 85 (manufactured by Nippon Nyukazai Co., Ltd.) was used as a nonionic surfactant instead of Softanol 120 (manufactured by Nippon Shokubai Co., Ltd.) in an amount of 0.75 mass equivalent relative to the raw material graphite. When the filtration performance was confirmed in the same manner as in the method described in , the filtration performance was found to be good.

(Comparative example 1)
When the filtration performance was confirmed in the same manner as described in Example 1 except that no flocculant was used and no nonionic surfactant (Softanol 120) was added, the filtration performance was very poor and the filter paper was clogged and could not be filtered.

(Comparative example 2)
As an example of using an anionic surfactant instead of a nonionic surfactant, 0.75 mass equivalent of Softanol 120 (manufactured by Nippon Shokubai Co., Ltd.) was replaced with the same equivalent amount of linear dodecylbenzene based on the raw material graphite. When the filtration performance was confirmed in the same manner as described in Example 1 except that sodium sulfonate (manufactured by Wako Pure Chemical Industries, Ltd.) was used, the filtration performance was very poor, and the filter paper was clogged, making filtration impossible. Ta.

<Dispersion of graphite oxide composite>
(Example 4)
100 g of water was added to the graphite oxide composite-containing wet cake obtained in Example 1 (equivalent to 1 g of raw graphite), stirred, and then ultrasonic waves were applied for 30 minutes to prepare an aqueous dispersion of graphite oxide composite. . When the aqueous dispersion was allowed to stand for 24 hours, no phase separation occurred and a uniform appearance was maintained, indicating very good dispersibility.

(Example 5)
An aqueous dispersion of a graphite oxide composite was prepared in the same manner as in Example 4, except that the wet cake containing the graphite oxide composite was obtained in Example 2, and then left to stand for 24 hours. As a result, the water dispersion maintained a uniform appearance and exhibited very good dispersibility.

(Example 6)
An aqueous dispersion of a graphite oxide composite was prepared in the same manner as in Example 4, except that the wet cake containing the graphite oxide composite was obtained in Example 3, and then left to stand for 24 hours. As a result, the water dispersion maintained a uniform appearance and exhibited very good dispersibility.

(Example 7)
A γ-butyrolactone dispersion of a graphite oxide composite was prepared in the same manner as in Example 4 except that the dispersion medium used was γ-butyrolactone, and when it was left to stand for 24 hours, a γ-butyrolactone dispersion was obtained. maintained a uniform appearance and exhibited very good dispersibility.

(Example 8)
Further water was added to the aqueous dispersion of the graphite oxide composite obtained in Example 4 so that the graphite equivalent amount was 0.66% by mass, and a tabletop ultrasonic cleaner (manufactured by Branson, Bransonic, A uniform aqueous dispersion of graphite oxide composite was obtained by applying ultrasonic waves for 30 minutes using a 405 W). By adding 7.5 mass equivalents of L-ascorbic acid (manufactured by Wako Pure Chemical Industries, Ltd.) to graphite as a reducing agent into the aqueous dispersion of the graphite oxide composite, and reacting at 70°C for 1 hour. I gave back. After the reaction, the mixture was filtered and washed with water until the filtrate became neutral using pH test paper. 100 g of water was added to the obtained graphite oxide composite-containing wet cake (equivalent to 1 g of raw graphite), stirred, and then ultrasonic waves were applied for 30 minutes to prepare an aqueous dispersion of the graphite oxide composite. When the obtained aqueous dispersion was allowed to stand for 24 hours, no phase separation occurred and a uniform appearance was maintained, indicating good dispersibility, but some aggregates were observed. When the graphite oxide composite obtained in Example 8 was further washed and the graphite oxide obtained was analyzed, the C/O ratio was 5.7.

From the results of Examples 1 to 3 and Comparative Examples 1 and 2, good purification efficiency was shown by adding a nonionic surfactant before the purification step. Furthermore, the results of Examples 4 to 8 showed that the carbon material composites (graphite oxide composites) obtained by the above purification method showed good dispersibility in various dispersion media. By the method for producing a carbon material composite of the present invention, a high quality carbon material composite can be easily obtained at low cost. Further, the obtained carbon material composite (carbon material composite comprising a nonionic surfactant and graphite oxide) can be dispersed very well in a dispersion medium.

Claims (5)

A method for producing a carbon material composite comprising a nonionic surfactant and graphite oxide, the method comprising:
The manufacturing method includes a step of oxidizing graphite using sulfuric acid in an amount such that the mass ratio of sulfuric acid to graphite (sulfuric acid/graphite) is 25 to 60 ;
The aqueous dispersion in which graphite oxide is dispersed , obtained in the oxidation step , and the hydrophobic group in an amount of 10 to 1000% by mass based on 100% by mass of graphite oxide in the aqueous dispersion are hydrocarbon groups. and a nonionic surfactant whose hydrophilic group is at least one selected from the group consisting of an alkylene oxide group, an ether group, an ester group, an amide group, and a hydroxyl group. a step of purifying the body by at least one method selected from the group consisting of filtration, decantation, centrifugation, and liquid separation extraction , and
A method for producing a carbon material composite, comprising a step of peeling off layers of graphite oxide contained in the carbon material composite refined in the refining step. 2. The method for producing a carbon material composite according to claim 1 , wherein the aqueous dispersion contains 1% by mass or more of sulfate ions based on 100% by mass of the aqueous dispersion. A carbon material composite comprising a nonionic surfactant and graphite oxide,
A carbon material composite characterized in that the graphite oxide has a ratio of the number of carbon atoms to the number of oxygen atoms (C/O) of 5.5 or less. A dispersion comprising the carbon material composite according to claim 3 dispersed in a dispersion medium. A method for producing graphite oxide, the method comprising:
The manufacturing method includes a step of oxidizing graphite using sulfuric acid in an amount such that the mass ratio of sulfuric acid to graphite (sulfuric acid/graphite) is 25 to 60 ;
The aqueous dispersion in which graphite oxide is dispersed , obtained in the oxidation step , and the hydrophobic group in an amount of 10 to 1000% by mass based on 100% by mass of graphite oxide in the aqueous dispersion are hydrocarbon groups. After mixing with a nonionic surfactant whose hydrophilic group is composed of at least one selected from the group consisting of an alkylene oxide group, an ether group, an ester group, an amide group, and a hydroxyl group, graphite oxide is mixed. , a step of purifying by at least one method selected from the group consisting of filtration, decantation, centrifugation, and liquid separation extraction , and
A method for producing graphite oxide, comprising a step of peeling off the layers of graphite oxide purified in the purification step.