JP6785463B2 - Method for producing graphene oxide, graphene oxide dispersion and graphene oxide - Google Patents
Method for producing graphene oxide, graphene oxide dispersion and graphene oxide Download PDFInfo
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本発明は、分散性が高く、構造欠陥の生成が抑制された酸化グラフェン、酸化グラフェン分散液及び酸化グラフェンの製造方法に関する。 The present invention relates to a graphene oxide, a graphene oxide dispersion, and a method for producing graphene oxide, which have high dispersibility and suppress the formation of structural defects.
グラフェンは、ベンゼン環が平面状（又は２次元状）に連なった構造を有しており、その構造に由来して、機械的特性、電気的特性、熱的特性などの種々の特性が優れているため、電気デバイスなどの様々な分野への利用が検討されている。しかし、疎水性のグラフェンを水性溶媒中に均一に分散させることが困難であるため、分散性を改善するために親水化処理を行う必要がある。親水化処理として、例えば、過マンガン酸カリウムなどの酸化剤を使用してグラフェンに親水基を導入する化学的酸化法が知られているが、強い酸化剤を使用するため、構造中に多くの欠陥が生じ、品質が劣化し易い。また、強い酸化剤を使用すると環境負荷が大きい。一方、分散性を高めるために界面活性剤などの種々の添加剤を溶媒中に添加することも考えられるが、添加剤は、粉体の純度を低下させ、グラフェンの機能及び特性を低下させる原因となる。 Graphene has a structure in which benzene rings are connected in a planar shape (or two-dimensional shape), and due to this structure, various properties such as mechanical properties, electrical properties, and thermal properties are excellent. Therefore, its use in various fields such as electrical devices is being considered. However, since it is difficult to uniformly disperse hydrophobic graphene in an aqueous solvent, it is necessary to carry out a hydrophilic treatment in order to improve the dispersibility. As a hydrophilic treatment, for example, a chemical oxidation method in which a hydrophilic group is introduced into graphene using an oxidizing agent such as potassium permanganate is known, but since a strong oxidizing agent is used, many are used in the structure. Defects occur and the quality tends to deteriorate. Moreover, the use of a strong oxidizing agent has a large environmental load. On the other hand, it is conceivable to add various additives such as a surfactant to the solvent in order to improve the dispersibility, but the additive reduces the purity of the powder and causes the function and characteristics of graphene to be deteriorated. It becomes.
特開２０１４−１５２０９５号公報（特許文献１）には、水溶液中に浸漬させた炭素電極間に、電圧１〜２ｋＶ、パルス幅０．５〜４μｓ、パルス周波数５〜５０ｋＨｚの条件でパルス電圧を印加してグロー放電プラズマを発生させると、炭素電極からグラフェンを形成することが開示されている。また、この文献には、欠陥の発生が抑制されたグラフェンを製造可能であることが記載されている。 According to Japanese Patent Application Laid-Open No. 2014-152095 (Patent Document 1), a pulse voltage is applied between carbon electrodes immersed in an aqueous solution under the conditions of a voltage of 1 to 2 kV, a pulse width of 0.5 to 4 μs, and a pulse frequency of 5 to 50 kHz. It is disclosed that when applied to generate a glow discharge plasma, graphene is formed from a carbon electrode. In addition, this document describes that graphene in which the occurrence of defects is suppressed can be produced.
しかし、この文献は、グラフェンの分散性を高めることについて記載されていない。 However, this document does not describe enhancing the dispersibility of graphene.
ＷＯ２００９／１１９０５９号（特許文献２）には、エタノール又は２−プロパノールの気液界面を挟んでプラズマを発生させ、エタノール又は２−プロパノールを分解させてグラフェンを製造する方法が開示されている。しかし、この文献のグラフェンは、ラマンスペクトルにおいて、構造欠陥に起因するＤバンドのピークが非常に大きく、導電性が低いと考えられ、有用でない。 WO2009 / 115909 (Patent Document 2) discloses a method for producing graphene by generating plasma across a gas-liquid interface of ethanol or 2-propanol and decomposing ethanol or 2-propanol. However, graphene in this document is not useful in the Raman spectrum because it has a very large D-band peak due to structural defects and is considered to have low conductivity.
特開２０１５−２２７２５３号公報（特許文献３）には、グラファイトロッドをトリアジン誘導体の水溶液に浸漬させ、パルスプラズマを印加すると、得られるグラフェンの表面にトリアジン誘導体が吸着し、水中で高い分散安定性を維持することが開示されている。 According to JP-A-2015-227253 (Patent Document 3), when a graphite rod is immersed in an aqueous solution of a triazine derivative and pulse plasma is applied, the triazine derivative is adsorbed on the surface of the obtained graphene and has high dispersion stability in water. Is disclosed to maintain.
しかし、この文献の方法では、グラフェンの分散安定性を維持するためには、トリアジンを必要とする。 However, the methods of this document require triazine to maintain the dispersion stability of graphene.
特許第５５０１３６２号公報（特許文献４）には、水などの液体に炭素系粉体を添加し、この液体の液面上にプラズマを生成すると、液面に設置された粉体の表面修飾が行われ、粉体と液体との親和性が高められ、液体を分散溶剤とする分散液が製造できることが開示されている。特開２０１３−１８８２号公報（特許文献５）には、水及び導電性付与剤を含む溶液にグラフェンを添加し、この溶液中にグロー放電を起こしてプラズマを発生させると、グラフェンに、カルボキシル基、ヒドロキシル基などの親水基を導入できることが開示されている。この文献の実施例には、水と、導電性付与剤としてメタノールとを含む混合溶液にグラフェンを添加し、３ｋＨｚ、１．２５ｋＶのパルス電圧を印加し、この溶液中にプラズマを発生させると、グラフェンが長時間に亘り分散状態を維持できることが記載されている。 According to Japanese Patent No. 5501362 (Patent Document 4), when a carbon-based powder is added to a liquid such as water and plasma is generated on the liquid surface of this liquid, the surface modification of the powder placed on the liquid surface is performed. It is disclosed that the affinity between the powder and the liquid is enhanced, and a dispersion liquid using the liquid as a dispersion solvent can be produced. According to Japanese Patent Application Laid-Open No. 2013-1882 (Patent Document 5), when graphene is added to a solution containing water and a conductivity-imparting agent and a glow discharge is caused in this solution to generate plasma, the graphene has a carboxyl group. , It is disclosed that a hydrophilic group such as a hydroxyl group can be introduced. In the examples of this document, graphene is added to a mixed solution containing water and methanol as a conductivity-imparting agent, a pulse voltage of 3 kHz and 1.25 kV is applied to generate plasma in this solution. It has been described that graphene can maintain a dispersed state for a long period of time.
しかし、これらの文献には、グラフェンを酸化しても、構造欠陥の生成が有効に抑制されることについて記載されていない。また、グラフェンの分散性をさらに高めるために所定の官能基（ヒドロキシル基、カルボキシル基など）濃度を有効に制御できることについて記載されていない。 However, these documents do not describe that oxidation of graphene effectively suppresses the formation of structural defects. Further, it is not described that a predetermined functional group (hydroxyl group, carboxyl group, etc.) concentration can be effectively controlled in order to further enhance the dispersibility of graphene.
従って、本発明の目的は、分散性が高く、構造欠陥の生成が抑制された酸化グラフェン、酸化グラフェン分散液及びその製造方法を提供することにある。 Therefore, an object of the present invention is to provide graphene oxide, a graphene oxide dispersion, and a method for producing the same, which have high dispersibility and suppress the formation of structural defects.
本発明の他の目的は、ヒドロキシル基濃度が高い酸化グラフェン、酸化グラフェン分散液及びその製造方法を提供することにある。 Another object of the present invention is to provide graphene oxide having a high concentration of hydroxyl groups, a graphene oxide dispersion, and a method for producing the same.
本発明のさらに他の目的は、生産性を向上でき、官能基（ヒドロキシル基、カルボキシル基など）の濃度分布を制御可能な酸化グラフェンの製造方法を提供することにある。 Still another object of the present invention is to provide a method for producing graphene oxide, which can improve productivity and can control the concentration distribution of functional groups (hydroxyl group, carboxyl group, etc.).
本発明者らは、前記課題を達成するため鋭意検討した結果、グラフェン構造を有する炭素材と水性分散媒とを含む懸濁液を、液中又は液面でプラズマ処理すると、ヒドロキシル基及び／又はカルボニル含有基が導入されているためか、分散性を高めることができ、かつ構造欠陥の生成が抑制されている酸化グラフェンを製造できることを見出し、本発明を完成した。 As a result of diligent studies to achieve the above problems, the present inventors have subjected to plasma treatment of a suspension containing a carbon material having a graphene structure and an aqueous dispersion medium in liquid or on the liquid surface to obtain hydroxyl groups and / or The present invention has been completed by finding that graphene oxide can be produced, which can enhance dispersibility and suppress the formation of structural defects, probably because a carbonyl-containing group is introduced.
すなわち、本発明の酸化グラフェンは、ヒドロキシル基及び／又はカルボニル含有基を有する酸化グラフェンであって、ラマンスペクトルにおいて、ＤバンドとＧバンドとの強度比（ＩＤ／ＩＧ）が、前者／後者（強度比）＝０．０１〜０．２である。 That is, the graphene oxide of the present invention is a graphene oxide having a hydroxyl group and / or a carbonyl-containing group, and the intensity ratio ( ID / IG ) of the D band to the G band in the Raman spectrum is the former / the latter. (Strength ratio) = 0.01 to 0.2.
本発明は、前記酸化グラフェンと水性分散媒とを含む酸化グラフェン分散液を含む。前記水性分散媒は、水であってもよい。 The present invention includes a graphene oxide dispersion containing the graphene oxide and an aqueous dispersion medium. The aqueous dispersion medium may be water.
本発明は、グラフェン構造を有する炭素材と水性分散媒とを含む懸濁液を、液中又は液面でプラズマ処理（特に液面でプラズマ処理）して、グラフェンにヒドロキシル基及び／又はカルボニル含有基を導入する酸化グラフェンの製造方法を含む。本発明の製造方法では、液面プラズマ処理に先立ち、懸濁液を超音波処理してもよい。また、パルス電源を用いて、パルス周波数０．１〜５０ｋＨｚ（特に０．５〜１．５ｋＨｚ）の条件で、液面でプラズマ処理してもよい。 In the present invention, a suspension containing a carbon material having a graphene structure and an aqueous dispersion medium is plasma-treated in liquid or at the liquid surface (particularly plasma treatment at the liquid surface), and graphene contains a hydroxyl group and / or carbonyl. It includes a method for producing graphene oxide into which a group is introduced. In the production method of the present invention, the suspension may be ultrasonically treated prior to the liquid level plasma treatment. Further, plasma treatment may be performed on the liquid surface using a pulse power source under the condition of a pulse frequency of 0.1 to 50 kHz (particularly 0.5 to 1.5 kHz).
本発明では、グラフェン構造を有する炭素材と水性分散媒とを含む懸濁液を、液中又は液面でプラズマ処理することにより酸化グラフェンを製造するため、グラフェンにヒドロキシル基及び／又はカルボニル含有基を導入して分散性を高めることができるとともに、構造欠陥が生成するのを抑制できる。また、消費電力を効率よく抑制できるため、生産性を向上でき、官能基濃度分布を制御できる。 In the present invention, in order to produce graphene oxide by plasma-treating a suspension containing a carbon material having a graphene structure and an aqueous dispersion medium in or on the liquid surface, graphene contains a hydroxyl group and / or a carbonyl group. Can be introduced to improve dispersibility and suppress the formation of structural defects. In addition, since power consumption can be efficiently suppressed, productivity can be improved and the functional group concentration distribution can be controlled.
［酸化グラフェン］
本発明の酸化グラフェンは、ヒドロキシル基及び／又はカルボニル含有基（特にヒドロキシル基及びカルボニル含有基）を含んでおり、分散性が高いという特色を有する。カルボニル含有基としては、例えば、カルボニル基、ホルミル基、カルボキシル基及び／又はこれらの組み合わせが例示でき、通常、カルボキシル基単独、又はカルボキシル基及びカルボニル基である場合が多い。尚、これらの官能基の有無は、例えば、ＦＴ−ＩＲ（フーリエ変換赤外分光光度計）にて各官能基由来のピークを観測することにより確認できる。
[Graphene oxide]
The graphene oxide of the present invention contains a hydroxyl group and / or a carbonyl-containing group (particularly a hydroxyl group and a carbonyl-containing group), and has a feature of high dispersibility. Examples of the carbonyl-containing group include a carbonyl group, a formyl group, a carboxyl group and / or a combination thereof, and usually, the carboxyl group alone or the carboxyl group and the carbonyl group are often used. The presence or absence of these functional groups can be confirmed, for example, by observing the peaks derived from each functional group with FT-IR (Fourier transform infrared spectrophotometer).
本発明の酸化グラフェンは、構造欠陥が少ないという特色も有する。本発明の酸化グラフェンは、ラマンスペクトルにおいて、Ｄバンド（又はＤピーク）とＧバンド（又はＧピーク）との強度比（ＩＤ／ＩＧ）が、前者／後者（強度比）＝０．０１〜０．２、好ましくは０．１８以下（例えば、０．０２〜０．１８など）、さらに好ましくは０．１５以下（例えば、０．０２５〜０．１５など）、特に０．１２以下（例えば、０．０５〜０．１など）であってもよい。前記Ｄバンドは、グラフェン構造中の格子欠陥などの無秩序構造に由来する１３５０ｃｍ−１付近のピークであり、Ｇバンドは、グラフェン構造の面内振動に由来する１５９０ｃｍ−１付近のピークである。本発明の酸化グラフェンは、ＩＤ／ＩＧが小さいため、炭素六員環中の構造欠陥が少ない。 The graphene oxide of the present invention is also characterized by having few structural defects. Graphene oxide of the present invention, in the Raman spectrum, D band (or D peak) and G band (or G peak) intensity ratio (I D / I G) is the former / the latter (intensity ratio) = 0.01 ~ 0.2, preferably 0.18 or less (eg 0.02 to 0.18), more preferably 0.15 or less (eg 0.025 to 0.15), especially 0.12 or less (eg, 0.025 to 0.15) For example, 0.05 to 0.1). The D band is a peak near 1350 cm -1 due to a disordered structure such as a lattice defect in the graphene structure, and the G band is a peak near 1590 cm -1 due to in-plane vibration of the graphene structure. Graphene oxide of the present invention, because I D / I G is small, less structural defects six-membered in the ring carbons.
本発明の酸化グラフェンは、ラマンスペクトルにおいて、Ｇバンド（又はＧピーク）と２Ｄバンド（又は２Ｄピーク）との強度比（ＩＧ／Ｉ２Ｄ）が、前者／後者（強度比）＝１〜３、好ましくは１．５〜２．５程度である。２Ｄバンドとは、２７００ｃｍ−１付近のピークであり、ＩＧ／Ｉ２Ｄが大きいことは、グラフェンの層数が大きいことを示す。 In the graphene oxide of the present invention, the intensity ratio ( IG / I 2D ) of the G band (or G peak) and the 2D band (or 2D peak) in the Raman spectrum is the former / the latter (intensity ratio) = 1 to 3. , Preferably about 1.5 to 2.5. And 2D band is a peak around 2700 cm -1, it I G / I 2D is large, indicating that the number of layers of graphene large.
［酸化グラフェンの製造方法］
本発明の酸化グラフェンは、グラフェン構造を有する炭素材（炭素材）と水性分散媒とを含む懸濁液を、液中又は液面プラズマ処理して、グラフェンにヒドロキシル基及び／又はカルボニル含有基（特にヒドロキシル基及びカルボニル含有基）を導入することにより得られる。
[Manufacturing method of graphene oxide]
The graphene oxide of the present invention is obtained by subjecting a suspension containing a carbon material (carbon material) having a graphene structure and an aqueous dispersion medium to a liquid or liquid surface plasma treatment, and the graphene is subjected to a hydroxyl group and / or a carbonyl-containing group ( In particular, it is obtained by introducing a hydroxyl group and a carbonyl-containing group).
前記炭素材としては、グラフェン構造を有すれば特に限定されず、例えば、グラファイト、グラフェンなどが例示でき、その形態も特に限定されず、例えば、粉末状、顆粒状の形態が例示できる。これらの材料は、市販品を使用してもよく、慣用の方法、例えば、マイクロ波ＣＶＤ法、常圧ＣＶＤ法などにより調製してもよい。 The carbon material is not particularly limited as long as it has a graphene structure, and examples thereof include graphite and graphene, and the form thereof is not particularly limited, and examples thereof include powder and granular forms. Commercially available products may be used for these materials, or they may be prepared by a conventional method, for example, a microwave CVD method, a normal pressure CVD method, or the like.
水性分散媒としては、例えば、水単独、水と水溶性溶媒との混合溶媒であってもよい。水溶性溶媒としては、例えば、アルコール類（例えば、メタノール、エタノールなど）、ケトン類（例えば、アセトンなど）、エーテル類（例えば、ジオキサン、テトラヒドロフランなど）、セロソルブ類、セロソルブアセテート類、カルビトール類、カルビトールアセテート類、ニトリル類（例えば、アセトニトリルなど）、アミド類（例えば、Ｎ，Ｎ−ジメチルホルムアミドなど）が例示できる。水溶性溶媒は、単独で又は２種以上組み合わせて使用できる。前記水性分散媒中の水含有量は、例えば、５０〜１００重量％であり、好ましくは８０重量％以上、さらに好ましくは９０重量％以上、特に１００重量％である。本発明の製造方法では、アルコール類などの水溶性溶媒を含有させなくても、前記炭素材を低環境負荷で有効に酸化できる。そのため、水性分散媒としては、水単独であるのがよい。 The aqueous dispersion medium may be, for example, water alone or a mixed solvent of water and a water-soluble solvent. Examples of the water-soluble solvent include alcohols (for example, methanol, ethanol, etc.), ketones (for example, acetone, etc.), ethers (for example, dioxane, tetrahydrofuran, etc.), cellosolves, cellosolve acetates, carbitols, and the like. Examples thereof include carbitol acetates, nitriles (for example, acetonitrile), and amides (for example, N, N-dimethylformamide). The water-soluble solvent can be used alone or in combination of two or more. The water content in the aqueous dispersion medium is, for example, 50 to 100% by weight, preferably 80% by weight or more, more preferably 90% by weight or more, and particularly 100% by weight. In the production method of the present invention, the carbon material can be effectively oxidized with a low environmental load without containing a water-soluble solvent such as alcohols. Therefore, water alone is preferable as the aqueous dispersion medium.
前記炭素材と前記水性分散媒との使用割合は、例えば、水性分散媒１００重量部に対し、１〜１００重量部、好ましくは５〜５０重量部、さらに好ましくは２０〜４０重量部程度であってもよい。 The ratio of the carbon material to the aqueous dispersion medium used is, for example, 1 to 100 parts by weight, preferably 5 to 50 parts by weight, and more preferably about 20 to 40 parts by weight with respect to 100 parts by weight of the aqueous dispersion medium. You may.
懸濁液は、さらにプラズマの発生を安定にかつ容易にするために電解質を含んでもよい。前記電解質としては、例えば、硫酸ナトリウムなどのアルカリ金属塩、塩化カリウムなどのアルカリ塩化物、水酸化ナトリウム、水酸化カリウムなどのアルカリ水酸化物などが例示できる。 The suspension may further contain an electrolyte to stabilize and facilitate the generation of plasma. Examples of the electrolyte include alkali metal salts such as sodium sulfate, alkaline chlorides such as potassium chloride, and alkaline hydroxides such as sodium hydroxide and potassium hydroxide.
前記懸濁液を液中又は液面プラズマ処理すると、液中又は液面で水由来のヒドロキシラジカルなどが生成し、このヒドロキシラジカルにより、グラフェン表面の疎水基がヒドロキシル基、カルボキシル基などに酸化されるためか、グラフェンの分散性を高めることができる。また、液中又は液面でプラズマ処理することは、構造欠陥の生成を抑制してグラフェンを酸化できるため有利である。さらに消費電力を抑え、生産性を向上できるため有利である。 When the suspension is treated with liquid or liquid surface plasma, water-derived hydroxy radicals and the like are generated in the liquid or on the liquid surface, and the hydroxyl radicals oxidize the hydrophobic groups on the graphene surface to hydroxyl groups, carboxyl groups and the like. Perhaps because of this, the dispersibility of graphene can be increased. Further, plasma treatment in or on the liquid surface is advantageous because it can suppress the formation of structural defects and oxidize graphene. Furthermore, it is advantageous because it can reduce power consumption and improve productivity.
液中プラズマ処理としては、慣用の液中プラズマ法（ソリューションプラズマ法）に基づく処理を利用でき、グロー放電によって、液体中の気泡の中にプラズマを発生できる方法であれば特に限定されない。通常、液中パルスプラズマ電源装置から高電圧パルス出力を電極に印加し、電極付近で沸騰した気泡内に液体の沸点以下のプラズマを発生させ、液体からラジカル種を生成する方法を利用できる。例えば、特開２０１４−１５２０９５号公報に記載の方法を利用できる。 The submerged plasma treatment is not particularly limited as long as it can use a treatment based on the conventional submerged plasma method (solution plasma method) and can generate plasma in bubbles in the liquid by glow discharge. Usually, a method can be used in which a high-voltage pulse output is applied to an electrode from a submerged pulse plasma power supply device, plasma below the boiling point of the liquid is generated in bubbles boiling near the electrode, and radical species are generated from the liquid. For example, the method described in JP2014-2152095 can be used.
液中プラズマ法は、市販の液中プラズマ装置を用いてもよく、実験装置を組立てて使用してもよい。実験装置の一例としては、密閉容器内の溶液中で対向可能な一対の炭素電極と、これらの炭素電極をパルスの形態で電圧印加するために、電気的に接続された外部回路とを有すればよく、必要に応じて、密閉容器にガスを排気するための排気口を設けてもよいし、外部回路は抵抗（充電抵抗、制限抵抗）、コンデンサ、変流器などを備えてもよい。 In the submerged plasma method, a commercially available submerged plasma apparatus may be used, or an experimental apparatus may be assembled and used. An example of an experimental device is a pair of carbon electrodes that can face each other in a solution in a closed container, and an external circuit that is electrically connected to apply a voltage to these carbon electrodes in the form of a pulse. If necessary, the closed container may be provided with an exhaust port for exhausting gas, and the external circuit may be provided with a resistor (charging resistance, limiting resistance), a capacitor, a current transformer, or the like.
パルス周波数は、例えば、０．１〜５０ｋＨｚの広い範囲から選択でき、例えば、０．５〜２５ｋＨｚ、好ましくは１〜１０ｋＨｚ、さらに好ましくは２．５〜７．５ｋＨｚ程度であってもよい。周波数が低すぎると、ヒドロキシラジカル濃度が低すぎるため、グラフェンのヒドロキシル基の導入効率が低下する虞がある。周波数が高すぎると、ヒドロキシラジカル濃度が高すぎるため、ラジカル同士が結合して損失反応が生じやすくなり、ヒドロキシル基の導入効率が低下する虞がある。 The pulse frequency can be selected from a wide range of, for example, 0.1 to 50 kHz, and may be, for example, 0.5 to 25 kHz, preferably 1 to 10 kHz, and more preferably about 2.5 to 7.5 kHz. If the frequency is too low, the hydroxyl radical concentration is too low, which may reduce the efficiency of introducing hydroxyl groups in graphene. If the frequency is too high, the hydroxy radical concentration is too high, so that radicals are likely to bond with each other and a loss reaction is likely to occur, which may reduce the efficiency of introducing hydroxyl groups.
なお、端子間距離、端子間印加電圧、パルス幅などの条件は、グラフェンの種類や割合などに応じて適宜選択できる。端子間距離は、例えば、０．１〜５ｍｍ、好ましくは０．１５〜３ｍｍ、さらに好ましくは０．２〜２ｍｍ程度であってもよい。端子間印加電圧は、端子間に印加されるプラズマが発生する前の電圧で、例えば、２〜１０ｋＶ、好ましくは３〜９ｋＶ、さらに好ましくは４〜８ｋＶ程度であってもよい。パルス幅は、例えば、１〜４０００ｎｓ、好ましくは５０〜２０００ｎｓ、さらに好ましくは１００〜１０００ｎｓ程度であってもよい。処理時間は、１〜１２０分、好ましくは５〜６０分、さらに好ましくは１０〜５０分程度、特に２０〜４０分程度であってもよい。 Conditions such as the distance between terminals, the voltage applied between terminals, and the pulse width can be appropriately selected according to the type and ratio of graphene. The distance between the terminals may be, for example, 0.1 to 5 mm, preferably 0.15 to 3 mm, and more preferably about 0.2 to 2 mm. The voltage applied between the terminals is a voltage before the plasma applied between the terminals is generated, and may be, for example, 2 to 10 kV, preferably 3 to 9 kV, and more preferably about 4 to 8 kV. The pulse width may be, for example, 1 to 4000 ns, preferably 50 to 2000 ns, and more preferably about 100 to 1000 ns. The treatment time may be 1 to 120 minutes, preferably 5 to 60 minutes, more preferably about 10 to 50 minutes, and particularly about 20 to 40 minutes.
本発明では、液中でプラズマ処理してもよいが、消費電力をさらに効率よく抑制し、生産効率を向上する観点から液面でプラズマ処理するのが好ましい。 In the present invention, plasma treatment may be performed in liquid, but plasma treatment on the liquid surface is preferable from the viewpoint of more efficiently suppressing power consumption and improving production efficiency.
液面プラズマ処理に先立ち、グラフェンの粒径を小さくしてグラフェン全体の表面積を大きくするために、懸濁液に超音波処理するのが好ましい。グラフェン全体の表面積を大きくしてから液面プラズマ処理を行うと、親水性官能基の導入率が向上するため有利である。 Prior to the liquid level plasma treatment, the suspension is preferably sonicated in order to reduce the particle size of the graphene and increase the surface area of the entire graphene. It is advantageous to increase the surface area of the entire graphene and then perform the liquid level plasma treatment because the introduction rate of hydrophilic functional groups is improved.
超音波の周波数、処理時間などの条件は、前記炭素材の種類や割合などに応じて適宜選択でき、周波数は、例えば、１〜５０ｋＨｚ程度であってもよく、処理時間は、例えば、１〜２０分程度であってもよい。超音波処理は、超音波洗浄器、超音波分散機などの慣用の装置を用いて行うことができる。 Conditions such as the frequency and processing time of the ultrasonic waves can be appropriately selected according to the type and ratio of the carbon material, the frequency may be, for example, about 1 to 50 kHz, and the processing time is, for example, 1 to 1. It may be about 20 minutes. The ultrasonic treatment can be performed by using a conventional device such as an ultrasonic cleaner or an ultrasonic disperser.
液面プラズマ処理としては、慣用の液面プラズマ法に基づく処理を利用でき、液面でプラズマを発生できる方法であれば特に限定されない。通常、直流電源プラズマ装置又はパルス電源プラズマ装置から高電圧出力を、液面から所定距離を置いて液面上に配置された針状電極と、液体底部に配置された接地電極とを一対とする電極に印加し、前記針状電極の先端と液面との間にプラズマを発生させる方法を利用できる。液面プラズマ法は、市販のプラズマ装置を用いることができ、例えば、特許文献２、４に記載の方法を利用できる。また、実験装置を組立てて使用してもよく、実験装置の一例としては、密閉容器中に液面から所定距離をおいて液面上に配置可能な針状電極と、容器の底部に配置された接地電極との一対の電極と、この一対の電極に電圧を印加するために、電気的に接続された外部回路とを有すればよい。前記実験装置では、必要に応じて、密閉容器には、ガスを供給するための供給口及びガスを排気するための排気口を設けてもよい。また、直流電源を使用する場合は、外部回路は、抵抗（バラスト抵抗、電流測定用抵抗）などを備えてもよく、パルス電源を使用する場合は、外部回路は、抵抗（充電抵抗、制限抵抗）、充電コンデンサ、変流器などを備えてもよい。 The liquid level plasma treatment is not particularly limited as long as it can use a treatment based on the conventional liquid level plasma method and can generate plasma at the liquid level. Usually, a high voltage output is output from a DC power plasma device or a pulse power plasma device, and a pair of needle-shaped electrodes arranged on the liquid surface at a predetermined distance from the liquid surface and a ground electrode arranged on the bottom of the liquid are paired. A method of applying to the electrode and generating plasma between the tip of the needle-shaped electrode and the liquid surface can be used. As the liquid level plasma method, a commercially available plasma device can be used, and for example, the methods described in Patent Documents 2 and 4 can be used. Further, the experimental device may be assembled and used, and as an example of the experimental device, a needle-shaped electrode that can be placed on the liquid surface at a predetermined distance from the liquid surface in a closed container and a needle-shaped electrode that can be placed on the liquid surface and arranged at the bottom of the container It suffices to have a pair of electrodes with the ground electrode and an external circuit electrically connected in order to apply a voltage to the pair of electrodes. In the experimental device, if necessary, the closed container may be provided with a supply port for supplying gas and an exhaust port for exhausting gas. When using a DC power supply, the external circuit may be provided with a resistor (ballast resistance, resistance for measuring current), etc., and when using a pulse power supply, the external circuit is a resistor (charging resistance, limiting resistance). ), Charging capacitor, current converter, etc. may be provided.
液面プラズマ処理では、電源が直流電源であってもよく、パルス電源であってもよい。 In the liquid level plasma treatment, the power source may be a DC power source or a pulse power source.
直流電源を用いる場合、針状電極先端と液面との距離、端子間印加電圧などの条件は、グラフェンの種類や割合などに応じて適宜選択できる。針状電極先端と液面との距離は、例えば、０．１〜１０ｍｍ、好ましくは０．５〜５ｍｍ、さらに好ましくは０．８〜２ｍｍ程度であってもよい。端子間印加電圧は、例えば、２〜１０ｋＶ、好ましくは３〜９ｋＶ、さらに好ましくは４〜８ｋＶ程度であってもよい。処理時間は、１〜１２０分、好ましくは５〜６０分、さらに好ましくは１０〜５０分程度、特に２０〜４０分程度であってもよい。また、密閉容器内で、空気中、不活性ガス（例えば、窒素、アルゴンなどの希ガス）下で液面プラズマ処理を行ってもよい。 When a DC power supply is used, conditions such as the distance between the tip of the needle-shaped electrode and the liquid level and the voltage applied between the terminals can be appropriately selected according to the type and ratio of graphene. The distance between the tip of the needle-shaped electrode and the liquid level may be, for example, 0.1 to 10 mm, preferably 0.5 to 5 mm, and more preferably 0.8 to 2 mm. The voltage applied between the terminals may be, for example, 2 to 10 kV, preferably 3 to 9 kV, and more preferably about 4 to 8 kV. The treatment time may be 1 to 120 minutes, preferably 5 to 60 minutes, more preferably about 10 to 50 minutes, and particularly about 20 to 40 minutes. Further, the liquid level plasma treatment may be performed in the air or under an inert gas (for example, a rare gas such as nitrogen or argon) in a closed container.
パルス電源を用いると、各条件（パルス周波数、端子間距離、端子間印加電圧、パルス幅、処理時間など）を適宜調整することにより、官能基分布、又は官能基濃度分布を制御できる。特に、パルス周波数を高めると、グラフェンに導入されたヒドロキシル基が、カルボニル基、ホルミル基、カルボキシル基へと酸化されるためか、官能基分布、又は官能基濃度分布を有効に制御できるため好ましい。 When the pulse power supply is used, the functional group distribution or the functional group concentration distribution can be controlled by appropriately adjusting each condition (pulse frequency, distance between terminals, voltage applied between terminals, pulse width, processing time, etc.). In particular, increasing the pulse frequency is preferable because the hydroxyl group introduced into graphene is oxidized to a carbonyl group, a formyl group, or a carboxyl group, or because the functional group distribution or the functional group concentration distribution can be effectively controlled.
パルス周波数は、例えば、０．１〜５０ｋＨｚの広い範囲から選択でき、生産性を向上でき、有効に酸化して酸化グラフェンの分散性を向上できるために、好ましくは０．２〜２０ｋＨｚ、さらに好ましくは０．３〜１０ｋＨｚ、特に０．４〜５ｋＨｚ、通常、０．５〜２ｋＨｚ（例えば、０．５〜１．５ｋＨｚ）程度であってもよい。 The pulse frequency can be selected from a wide range of, for example, 0.1 to 50 kHz, can improve productivity, and can be effectively oxidized to improve the dispersibility of graphene oxide. Therefore, the pulse frequency is preferably 0.2 to 20 kHz, more preferably 0.2 to 20 kHz. May be 0.3 to 10 kHz, particularly 0.4 to 5 kHz, usually about 0.5 to 2 kHz (for example, 0.5 to 1.5 kHz).
端子間距離は、例えば、０．１〜１ｍｍ、好ましくは０．１５〜０．５ｍｍ、さらに好ましくは０．２〜０．４ｍｍ程度であってもよい。端子間印加電圧は、端子間に印加されるプラズマが発生する前の電圧で、例えば、２〜１０ｋＶ、好ましくは３〜９ｋＶ、さらに好ましくは４〜８ｋＶ程度であってもよい。パルス幅は、例えば、１〜４０００ｎｓ、好ましくは５０〜２０００ｎｓ、さらに好ましくは１００〜１０００ｎｓ程度であってもよい。処理時間は、１〜１２０分、好ましくは５〜６０分、さらに好ましくは１０〜５０分程度、特に２０〜４０分程度であってもよい。また、密閉容器内で、空気中、不活性ガス雰囲気（例えば、窒素、アルゴンなどの希ガス）下で液面プラズマ処理を行ってもよい。 The distance between the terminals may be, for example, 0.1 to 1 mm, preferably 0.15 to 0.5 mm, and more preferably 0.2 to 0.4 mm. The voltage applied between the terminals is a voltage before the plasma applied between the terminals is generated, and may be, for example, 2 to 10 kV, preferably 3 to 9 kV, and more preferably about 4 to 8 kV. The pulse width may be, for example, 1 to 4000 ns, preferably 50 to 2000 ns, and more preferably about 100 to 1000 ns. The treatment time may be 1 to 120 minutes, preferably 5 to 60 minutes, more preferably about 10 to 50 minutes, and particularly about 20 to 40 minutes. Further, the liquid level plasma treatment may be performed in the air or in an inert gas atmosphere (for example, a rare gas such as nitrogen or argon) in a closed container.
本発明の製造方法では、分散液を攪拌しつつ、液面又は液中でプラズマ処理を行ってもよい。 In the production method of the present invention, plasma treatment may be performed on the liquid surface or in the liquid while stirring the dispersion liquid.
本発明の製造方法では、プラズマ処理を行った後、分散性をさらに高めるために超音波処理を行ってもよい。超音波の周波数、処理時間などの条件は、前記炭素材の種類や割合などに応じて適宜選択でき、周波数は、例えば、１〜５０ｋＨｚ程度であってもよく、処理時間は、例えば、１〜２０分程度であってもよい。超音波処理は、超音波洗浄器、超音波分散機などの慣用の装置を用いて行うことができる。 In the production method of the present invention, after plasma treatment, ultrasonic treatment may be performed in order to further enhance the dispersibility. Conditions such as the frequency and processing time of the ultrasonic waves can be appropriately selected according to the type and ratio of the carbon material, the frequency may be, for example, about 1 to 50 kHz, and the processing time is, for example, 1 to 1. It may be about 20 minutes. The ultrasonic treatment can be performed by using a conventional device such as an ultrasonic cleaner or an ultrasonic disperser.
本発明の製造方法では、さらに濾過、遠心分離処理により、分散液を精製してもよい。 In the production method of the present invention, the dispersion may be further purified by filtration and centrifugation.
［酸化グラフェン分散液］
本発明の酸化グラフェン分散液は、本発明の前記酸化グラフェンと、水性分散媒とを含む。水性分散媒としては、本発明の製造方法で例示した水性分散媒が例示できる。
[Graphene oxide dispersion]
The graphene oxide dispersion of the present invention contains the graphene oxide of the present invention and an aqueous dispersion medium. As the aqueous dispersion medium, the aqueous dispersion medium exemplified in the production method of the present invention can be exemplified.
酸化グラフェンの割合は、例えば、水性分散媒１００重量部に対し、０．１〜１００重量部、好ましくは１〜５０重量部、さらに好ましくは５〜３０重量部程度であってもよい。 The ratio of graphene oxide may be, for example, 0.1 to 100 parts by weight, preferably 1 to 50 parts by weight, and more preferably 5 to 30 parts by weight with respect to 100 parts by weight of the aqueous dispersion medium.
以下に、実施例に基づいて本発明をより詳細に説明するが、本発明はこれらの実施例によって限定されるものではない。 Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.
（グラフェン分散液の調製）
［実施例１〜４］
純水２０ｍＬにグラファイト５ｍｇを添加した懸濁液に、２３℃で超音波（周波数２０ｋＨｚ）を１０分照射した後、実施例１については、図７に示す液面直流電源プラズマ装置を組み立てて用い、実施例２〜４については、図８に示す液面パルス電源プラズマ装置を組み立てて用いて、表１に示す条件で液面プラズマ処理を行った。プラズマ処理液を２３℃で超音波（周波数２０ｋＨｚ）を５分照射して分散液を得た。
(Preparation of graphene dispersion)
[Examples 1 to 4]
A suspension in which 5 mg of graphite was added to 20 mL of pure water was irradiated with ultrasonic waves (frequency 20 kHz) for 10 minutes at 23 ° C., and then, in Example 1, the liquid level DC power supply plasma apparatus shown in FIG. 7 was assembled and used. In Examples 2 to 4, the liquid level pulse power supply plasma apparatus shown in FIG. 8 was assembled and used, and the liquid level plasma treatment was performed under the conditions shown in Table 1. The plasma treatment liquid was irradiated with ultrasonic waves (frequency 20 kHz) at 23 ° C. for 5 minutes to obtain a dispersion liquid.
［実施例５］
純水５０ｍＬに、グラファイト１５ｍｇを添加した懸濁液に、２３℃で超音波（周波数２０ｋＨｚ）を１０分照射した後、図９に示す液中パルス電源プラズマ装置を組み立てて用い、表１に示す条件で液中プラズマ処理を行った。プラズマ処理液を２３℃で超音波（周波数２０ｋＨｚ）を５分照射して分散液を得た。
[Example 5]
A suspension in which 15 mg of graphite was added to 50 mL of pure water was irradiated with ultrasonic waves (frequency 20 kHz) at 23 ° C. for 10 minutes, and then the submerged pulse power plasma device shown in FIG. 9 was assembled and used, as shown in Table 1. Submerged plasma treatment was performed under the conditions. The plasma treatment liquid was irradiated with ultrasonic waves (frequency 20 kHz) at 23 ° C. for 5 minutes to obtain a dispersion liquid.
（ＵＶスペクトル測定）
実施例１〜３及び５の分散液（処理時間２０分）を１．５時間静置した後、上澄み液の吸光度を紫外可視分光光度計（日本分光（株），Ｖ−６３０）を用いて測定したところ、実施例１〜３及び５のグラフェン由来の２５３ｎｍにピークを確認した。このことからグラフェンの分散性が向上したことがわかった。
(UV spectrum measurement)
After allowing the dispersions (treatment time 20 minutes) of Examples 1 to 5 to stand for 1.5 hours, the absorbance of the supernatant was measured using an ultraviolet-visible spectrophotometer (JASCO Corporation, V-630). As a result of measurement, a peak was confirmed at 253 nm derived from graphene of Examples 1 to 5 and 5. From this, it was found that the dispersibility of graphene was improved.
（ＦＴ−ＩＲ、ラマン分光評価用サンプルの調製）
各分散液を回転速度５０００ｒｐｍで１０分間、遠心処理を行い、グラフェンと水とをある程度分離させた後、定温乾燥器を用いて、３０℃、２４時間乾燥し、水を蒸発させ、グラフェンからなる評価用サンプルを得た。
(FT-IR, preparation of sample for Raman spectroscopic evaluation)
Each dispersion is centrifuged at a rotation speed of 5000 rpm for 10 minutes to separate graphene and water to some extent, and then dried at 30 ° C. for 24 hours using a constant temperature dryer to evaporate the water and consist of graphene. An evaluation sample was obtained.
各評価用サンプル（グラフェン）を用いてラマン分光測定及びＦＴ−ＩＲ測定を行った。なお、ＦＴ−ＩＲ測定は、ＫＢｒ錠剤法により行った。測定サンプルとしては、ＫＢｒ４０ｍｇに対して各評価用サンプル１ｍｇの割合で混合し、混合物を４ＭＰａで１分間圧縮して得られたペレットを測定サンプルとした。 Raman spectroscopic measurement and FT-IR measurement were performed using each evaluation sample (graphene). The FT-IR measurement was performed by the KBr tablet method. As a measurement sample, a pellet obtained by mixing 40 mg of KBr at a ratio of 1 mg of each evaluation sample and compressing the mixture at 4 MPa for 1 minute was used as a measurement sample.
図１〜５に実施例１〜５（実施例１〜３及び５は、処理時間２０分、実施例４は、処理時間１０分）のＦＴ−ＩＲ測定結果を示す。図１〜５に示すように、実施例１〜５のいずれもが、３０００〜３７００ｃｍ−１のヒドロキシル基のピーク強度が処理前と比較して増大していることを確認した。 FIGS. 1 to 5 show the FT-IR measurement results of Examples 1 to 5 (Examples 1 to 5 have a processing time of 20 minutes, and Example 4 has a processing time of 10 minutes). As shown in FIGS. 1 to 5, in all of Examples 1 to 5, it was confirmed that the peak intensity of the hydroxyl group of 3000 to 3700 cm -1 was increased as compared with that before the treatment.
次に、実施例１〜３について、横軸の供給電力量に対し、ＦＴ−ＩＲスペクトルのヒドロキシル基のピーク値を縦軸にとり、線形近似して傾きを比較した。結果を図６に示す。この結果、実施例２（パルス周波数１ｋＨｚ）のパルス放電プラズマの傾きが最も高く、親水化処理に対するエネルギー効率が優れていることを確認した。パルス放電は、直流放電に比べ、電子のエネルギーが高いため、ヒドロキシルラジカルを生成し易く、パルス周波数１ｋＨｚで処理するのが、パルス周波数５ｋＨｚで処理するよりも、ヒドロキシルラジカル濃度が低いため、ヒドロキシラジカルの損失反応が減少したと考えられる。 Next, for Examples 1 to 3, the peak value of the hydroxyl group in the FT-IR spectrum was taken on the vertical axis with respect to the electric energy supplied on the horizontal axis, and the slopes were compared by linear approximation. The results are shown in FIG. As a result, it was confirmed that the inclination of the pulse discharge plasma of Example 2 (pulse frequency 1 kHz) was the highest and the energy efficiency for the hydrophilic treatment was excellent. Compared to DC discharge, pulse discharge has higher electron energy, so it is easier to generate hydroxyl radicals, and processing at a pulse frequency of 1 kHz has a lower hydroxyl radical concentration than processing at a pulse frequency of 5 kHz, so hydroxy radicals. It is considered that the loss reaction of
ラマン分光測定結果に基づき、ＤバンドとＧバンドとの強度比（ＩＤ／ＩＧ）及びＧバンドと２Ｄバンドとの強度比（ＩＧ／Ｉ２Ｄ）を算出した。結果をそれぞれ表２及び表３に示す。なお、未処理の（プラズマ処理されていない）グラフェンについて、ラマン分光測定を行ったところ、ＩＤ／ＩＧが、０．０４であり、ＩＧ／Ｉ２Ｄが、１．６３であった。 Based on the Raman spectroscopic measurement results, the intensity ratio between the D band and the G band ( ID / IG ) and the intensity ratio between the G band and the 2D band ( IG / I 2D ) were calculated. The results are shown in Tables 2 and 3, respectively. Note that the unprocessed (not plasma treated) graphene was subjected to Raman spectrometry, I D / I G is a 0.04, I G / I 2D was 1.63.
表２に示すように、実施例１〜５のいずれにおいても、ＩＤ／ＩＧが低く、構造欠陥が少ないことを確認できた。 As shown in Table 2, it was confirmed that the ID / IG was low and the number of structural defects was small in all of Examples 1 to 5.
本発明の酸化グラフェンは、導電材料などのエレクトロニクス材料、リチウムイオン二次電池やキャパシタなどの電極材料（例えば、スーパーキャパシタ、燃料電池用電解質、電極など）センサー構成部材、導電性断熱体、電磁場シールド材料、プリンター用導電ロール、超伝導電流リードなどの種々の分野に利用できる。 The graphene oxide of the present invention is an electronic material such as a conductive material, an electrode material such as a lithium ion secondary battery or a capacitor (for example, a supercapacitor, an electrolyte for a fuel cell, an electrode, etc.), a sensor component, a conductive heat insulator, and an electromagnetic field shield. It can be used in various fields such as materials, conductive rolls for printers, and superconducting current leads.
Claims (4)
グラフェン構造を有する炭素材と水性分散媒とを含む懸濁液を、液面でプラズマ処理して、グラフェンにヒドロキシル基及び／又はカルボニル含有基を導入する製造方法。 And having a hydroxyl group and / or carbonyl-containing groups, in the Raman spectrum intensity ratio between D band and G band (I D / I G) is the former / the latter (intensity ratio) = at 0.01 to 0.2 A method for producing graphene oxide
A suspension containing a carbon material and an aqueous dispersion medium having a graphene structure, and a plasma treatment with the liquid surface, forming methods made you introduce a hydroxyl group and / or carbonyl-containing groups to graphene.
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