JP2012131691A - Expanded graphite and method for producing the same - Google Patents
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本発明は、剥離によりグラフェンやグラフェンライクシート（薄片化黒鉛）を容易に得ることを可能とする膨張化黒鉛及びその製造方法に関する。 The present invention relates to expanded graphite that makes it possible to easily obtain graphene and graphene-like sheets (exfoliated graphite) by peeling and a method for producing the same.
黒鉛は、多数のグラフェンが積層されてなる積層体である。二次元物質であるグラフェンは、２×１０５Ｖｓ−１程度の高い電子移動度を有するなど、特異な電子物性を有する。従って、グラフェンは、電極材料や透明導電膜などへの応用が期待されている。 Graphite is a laminate in which many graphenes are laminated. Graphene, which is a two-dimensional material, has unique electronic properties such as high electron mobility of about 2 × 10 5 Vs −1 . Accordingly, graphene is expected to be applied to electrode materials and transparent conductive films.
黒鉛からグラフェンをあるいは黒鉛よりもグラフェン積層数が少ない薄片化黒鉛すなわちグラフェンライクシートを得るために、様々な方法が提案されている。例えば、下記の非特許文献１には、黒鉛に機械的剥離力を与えることにより、黒鉛からグラフェンまたは薄片化黒鉛を得る方法が開示されている。また、下記の非特許文献２には、黒鉛を酸化してなる酸化黒鉛からグラフェンを剥離する方法が開示されている。さらに、下記の非特許文献３には、ＣＶＤ法を利用して、金属基板上に炭素を成膜しグラフェンを形成する方法が開示されている。 Various methods have been proposed to obtain exfoliated graphite, that is, a graphene-like sheet, in which graphene is made of graphite or has a smaller number of graphene layers than graphite. For example, the following Non-Patent Document 1 discloses a method of obtaining graphene or exfoliated graphite from graphite by applying mechanical peeling force to the graphite. Non-Patent Document 2 below discloses a method of peeling graphene from graphite oxide obtained by oxidizing graphite. Further, Non-Patent Document 3 below discloses a method of forming graphene by forming a carbon film on a metal substrate using a CVD method.
しかしながら、従来の黒鉛からグラフェンあるいは薄片化黒鉛を得る方法では、グラフェンあるいは薄片化黒鉛を黒鉛から大量にかつ容易に剥離することはできなかった。電極材料や導電膜などの工業材料へ応用する場合、大面積のグラフェンあるいは薄片化黒鉛を大量に得ることが強く求められている。 However, in the conventional method of obtaining graphene or exfoliated graphite from graphite, the graphene or exfoliated graphite cannot be easily peeled off in large quantities from graphite. When applied to industrial materials such as electrode materials and conductive films, it is strongly required to obtain large amounts of graphene or exfoliated graphite in large quantities.
本発明の目的は、グラフェンまたは薄片化黒鉛を大量にかつ容易に得ることを可能とする膨張化黒鉛及びその製造方法を提供することにある。 An object of the present invention is to provide expanded graphite and a method for producing the expanded graphite that can easily obtain a large amount of graphene or exfoliated graphite.
本発明に係る膨張化黒鉛は、グラフェン積層体のグラフェン間に層間物質が挿入された膨張化黒鉛であって、ＸＲＤパターンにおける２θ（ＣｕＫα）が８度〜１２度の範囲に現れる回折ピークを有し、２θ（ＣｕＫα）が２５度〜２７度の範囲の回折ピーク高さが０カウント以上２００カウント以下であって、前記２θ（ＣｕＫα）が８度〜１２度の範囲に現れる回折ピークの高さが１０カウント以上５００カウント以下の範囲にある。 The expanded graphite according to the present invention is an expanded graphite in which an interlayer material is inserted between graphenes of a graphene laminate, and has a diffraction peak in which 2θ (CuKα) in the XRD pattern appears in the range of 8 degrees to 12 degrees. The height of the diffraction peak when 2θ (CuKα) is in the range of 25 ° to 27 ° is 0 to 200 counts, and the height of the diffraction peak where 2θ (CuKα) appears in the range of 8 ° to 12 °. Is in the range of 10 to 500 counts.
カウント数は測定条件によっても変わるため、本発明におけるカウント数は次の条件でのＸＲＤ測定における回折ピークを指すものとする。管電圧４０ｋＶ、管電流４０ｍＡ、スキャンスピード０．２５°／分、発散スリット０．５°、散乱スリット０．５°、受光スリット０．１５ｍｍ、管球ＣｕＫα。 Since the count number varies depending on the measurement conditions, the count number in the present invention refers to a diffraction peak in XRD measurement under the following conditions. Tube voltage 40 kV, tube current 40 mA, scan speed 0.25 ° / min, divergence slit 0.5 °, scattering slit 0.5 °, light receiving slit 0.15 mm, tube CuKα.
上記測定条件において、２θ（ＣｕＫα）が８度〜１２度の範囲内に現れる回折ピーク
の高さが１０カウント以上５００カウント以下の範囲にあることは、本発明の膨張化黒鉛においては、対向し合っているグラフェン間の角度が様々な範囲にあるものを含んでいることを意味する。すなわち、対向しているグラフェンの主面間が成す角度が様々な角度となっていると考えられる。２θ（ＣｕＫα）が８度〜１２度の範囲内に現れる回折ピーク高さの、より好ましい範囲は１０カウント以上２００カウント以下であり、更に好ましい範囲は１０カウント以上１００カウント以下の範囲である。
In the above measurement conditions, the height of the diffraction peak where 2θ (CuKα) appears in the range of 8 degrees to 12 degrees is in the range of 10 counts to 500 counts. It means that the angle between the matching graphenes is in various ranges. That is, it is considered that the angles formed between the main surfaces of the opposing graphene are various angles. A more preferable range of the diffraction peak height at which 2θ (CuKα) appears in the range of 8 degrees to 12 degrees is 10 counts to 200 counts, and a more preferable range is a range of 10 counts to 100 counts.
本発明に係る膨張化黒鉛のある特定の局面では、前記グラフェンは、酸化グラフェンである。 In a specific aspect of the expanded graphite according to the present invention, the graphene is graphene oxide.
本発明に係る膨張化黒鉛では、上記層間物質として少なくとも１種のイオンが挿入されている。上記のイオンとしては、硝酸イオン、硫酸イオン、ギ酸イオン及び酢酸イオンなどが挙げられる。これらのイオンが挿入されることにより、膨張化黒鉛からグラフェンあるいは薄片化黒鉛をより一層容易にかつ確実に剥離することができる。 In the expanded graphite according to the present invention, at least one ion is inserted as the interlayer material. Examples of the ions include nitrate ions, sulfate ions, formate ions, and acetate ions. By inserting these ions, graphene or exfoliated graphite can be more easily and reliably peeled from expanded graphite.
本発明に係る膨張化黒鉛の製造方法は、黒鉛を酸性電解質水溶液中に浸漬し、該黒鉛を作用極とし、対照極との間に、自然電位以外に０．６Ｖ〜０．８Ｖの範囲の直流電圧を、４８時間以上、１０００時間以下印加する電気化学的処理を行うことを特徴とする。このような電気化学的処理により、本発明に係る膨張化黒鉛を確実に得ることができる。 In the method for producing expanded graphite according to the present invention, graphite is dipped in an acidic electrolyte aqueous solution, the graphite is used as a working electrode, and in the range of 0.6 V to 0.8 V in addition to the natural potential between the reference electrode and the graphite. An electrochemical treatment is performed in which a DC voltage is applied for 48 hours or more and 1000 hours or less. By such electrochemical treatment, the expanded graphite according to the present invention can be obtained reliably.
本発明に係る膨張化黒鉛では、ＸＲＤパターンにおける２θ（ＣｕＫα）が８度〜１２度の範囲に現れる回折ピークを有し、２θ（ＣｕＫα）が２５度〜２７度の範囲の回折ピーク高さが０カウント以上、２００カウント以下であるので、元の黒鉛の層構造はほとんど消失し、グラフェン間の距離が層間物質の挿入により広げられた膨張化黒鉛であり、かつ２θ（ＣｕＫα）が８度〜１２度の範囲に現れる回折ピークの高さが１０カウント以上５００カウント以下の範囲にあるため、対向し合っているグラフェンの主面間の角度が様々な範囲にある。従って、対向し合っているグラフェン間の角度が様々であるため、剥離力を与えることにより、本発明の膨張化黒鉛からグラフェンまたはグラフェン積層体である薄片化黒鉛を容易に得ることができる。よって、本発明によれば、グラフェンまたは薄片化黒鉛を黒鉛から大量にかつ安定に製造することが可能となる。 The expanded graphite according to the present invention has a diffraction peak where 2θ (CuKα) in the XRD pattern appears in the range of 8 ° to 12 °, and the diffraction peak height in the range of 2θ (CuKα) of 25 ° to 27 °. Since it is 0 count or more and 200 count or less, the original graphite layer structure is almost lost, the distance between the graphenes is expanded graphite, and 2θ (CuKα) is 8 degrees to Since the height of the diffraction peak appearing in the range of 12 degrees is in the range of 10 counts or more and 500 counts or less, the angles between the main faces of the graphene facing each other are in various ranges. Therefore, since the angles between the graphenes facing each other are various, exfoliated graphite which is a graphene or a graphene laminate can be easily obtained from the expanded graphite of the present invention by applying a peeling force. Therefore, according to the present invention, it is possible to stably produce graphene or exfoliated graphite in large quantities from graphite.
以下、本発明の実施形態を説明することにより、本発明の詳細を明らかにする。 Hereinafter, the details of the present invention will be clarified by describing embodiments of the present invention.
本明細書において、膨張化黒鉛とは、元の黒鉛に層間物質が挿入され、グラフェン間の
距離が広げられた黒鉛をいうものとする。また、本明細書においては、炭素六角網平面からなる１枚のシート状物質をグラフェンとする。薄片化黒鉛とは、グラフェン積層体であって、上記膨張化黒鉛を剥離することにより得られた、膨張化黒鉛よりもグラフェン積層数が少ない積層体、すなわちグラフェンライクシートをいうものとする。
In the present specification, expanded graphite refers to graphite in which an interlayer material is inserted into original graphite and the distance between graphenes is increased. Moreover, in this specification, the sheet-like substance which consists of a carbon hexagonal mesh plane is made into graphene. Exfoliated graphite refers to a graphene laminate, which is obtained by peeling off the expanded graphite, and is a laminate having a smaller number of graphene layers than expanded graphite, that is, a graphene-like sheet.
また、本発明の膨張化黒鉛に含まれるグラフェンは、酸化グラフェンであってもよい。 The graphene contained in the expanded graphite of the present invention may be graphene oxide.
本発明に係る膨張化黒鉛を得るには、まず、黒鉛を作用極とし、該作用極をＰｔなどからなる対照極とともに、酸性電解質水溶液中に浸漬し、電気分解する。それによって、黒鉛すなわち層状黒鉛のグラフェン間に酸性電解質イオンをインターカレートすることができ、層間すなわちグラフェン間を広げることができる。 In order to obtain expanded graphite according to the present invention, first, graphite is used as a working electrode, and the working electrode together with a reference electrode made of Pt or the like is immersed in an acidic electrolyte aqueous solution and electrolyzed. Thereby, acidic electrolyte ions can be intercalated between graphene of graphite, that is, layered graphite, and the interlayer, that is, between graphenes, can be widened.
上記電解質水溶液としては、硝酸、硫酸などを用いることができる。それによって、硝酸イオンや硫酸イオンなどをグラフェン間に挿入することができる。 Nitric acid, sulfuric acid, etc. can be used as the electrolyte aqueous solution. Thereby, nitrate ions, sulfate ions, and the like can be inserted between the graphenes.
本発明の特徴は、上記電気化学的処理に際し、自然電位以外に０．６Ｖ〜０．８Ｖの直流電圧を４８時間以上、１０００時間以下印加することにある。自然電位以外の直流電圧の範囲が、この範囲内にあれば、膨張化黒鉛のグラフェン間に硝酸イオンや硫酸イオンなどの酸性電解質イオンを確実にインターカレートすることができる。それによって、本発明に従って、対向し合っているグラフェンの主面間の角度が様々な範囲にある本発明の膨張化黒鉛を確実に得ることができる。より好ましくは、上記電気化学的処理に際し、自然電位以外に０．６Ｖ〜０．７Ｖの直流電圧を印加する。 A feature of the present invention resides in that a DC voltage of 0.6 V to 0.8 V is applied for 48 hours or more and 1000 hours or less in addition to the natural potential in the electrochemical treatment. If the DC voltage range other than the natural potential is within this range, acidic electrolyte ions such as nitrate ions and sulfate ions can be reliably intercalated between the graphenes of the expanded graphite. Thereby, according to the present invention, the expanded graphite of the present invention in which the angles between the main surfaces of the graphenes facing each other are in various ranges can be reliably obtained. More preferably, in the electrochemical treatment, a DC voltage of 0.6 V to 0.7 V is applied in addition to the natural potential.
なお、自然電位以外の直流電圧印加時間が、４８時間以上であればよいが、長すぎると生産性が低下し、かつ電解質イオンをインターカレートする効果も飽和する。従って、自然電位以外の直流電圧印加時間は１０００時間以下とすればよい。 The DC voltage application time other than the natural potential may be 48 hours or longer, but if it is too long, the productivity is lowered and the effect of intercalating electrolyte ions is saturated. Therefore, the DC voltage application time other than the natural potential may be 1000 hours or less.
上記のように、自然電位以外に０．６Ｖ〜０．８Ｖの直流電圧を４８時間以上印加することにより、得られる膨張化黒鉛の酸化度が上昇する。膨張化黒鉛の酸化度が高くなると、膨張化黒鉛のグラフェン面のエッジ部分には、水酸基やカルボキシル基が付与される。そのため、本発明によれば、他の物質の反応性に富む膨張化黒鉛を得ることができる。 As described above, by applying a DC voltage of 0.6 V to 0.8 V in addition to the natural potential for 48 hours or more, the degree of oxidation of the obtained expanded graphite increases. When the degree of oxidation of the expanded graphite increases, a hydroxyl group or a carboxyl group is imparted to the edge portion of the graphene surface of the expanded graphite. Therefore, according to the present invention, expanded graphite rich in the reactivity of other substances can be obtained.
上記電解質水溶液の濃度は、黒鉛に電解質イオンをインターカレートするには、その酸化度に依存するため、特に限定されないが、０．５〜２０モル／リットルが好ましい。上記電解質水溶液が酸化力の強い電解質の場合は、高い電解質濃度が好ましい。上記電解質水溶液が酸化力の弱い電解質の場合は、低い電解質濃度が好ましい。上記電解質水溶液が硝酸水溶液の場合には、上記電解質水溶液の濃度は１０〜１３モル／リットルが好ましい。上記電解質水溶液が硫酸水溶液の場合には、上記電解質水溶液の濃度は０．５〜５モル／リットルが好ましい。上記電解質水溶液がギ酸水溶液の場合には、上記電解質水溶液の濃度は０．５〜５モル／リットルが好ましい。この範囲内であれば、電解質イオンをより一層確実にグラフェン間にインターカレートすることができる。 The concentration of the aqueous electrolyte solution is not particularly limited because it depends on the degree of oxidation for intercalating electrolyte ions into graphite, but is preferably 0.5 to 20 mol / liter. When the aqueous electrolyte solution is an electrolyte having a strong oxidizing power, a high electrolyte concentration is preferable. When the aqueous electrolyte solution is an electrolyte with weak oxidizing power, a low electrolyte concentration is preferable. When the aqueous electrolyte solution is an aqueous nitric acid solution, the concentration of the aqueous electrolyte solution is preferably 10 to 13 mol / liter. When the aqueous electrolyte solution is an aqueous sulfuric acid solution, the concentration of the aqueous electrolyte solution is preferably 0.5 to 5 mol / liter. When the aqueous electrolyte solution is a formic acid aqueous solution, the concentration of the aqueous electrolyte solution is preferably 0.5 to 5 mol / liter. Within this range, electrolyte ions can be intercalated between graphenes more reliably.
また、上記電気分解に際しての電解質水溶液の温度は特に限定されず、５度〜４５度程度の温度とすればよい。 The temperature of the electrolyte aqueous solution during the electrolysis is not particularly limited, and may be a temperature of about 5 to 45 degrees.
本願発明者らは、上記のように、電気化学的処理により膨張化黒鉛を得るにあたり、電圧印加条件を種々検討した結果、上記のように、自然電位以外の直流電圧の値を０．６Ｖ〜０．８Ｖの範囲かつ印加時間を４８時間以上とすれば、本発明に従って、対向し合っているグラフェンの主面間の角度が様々な膨張化黒鉛を安定にかつ確実に得ることを見出し、本発明を成すに至った。電圧印加時間はより好ましくは６０時間以上であり、更に好ましくは８０時間以上である。 As described above, the inventors of the present application studied various voltage application conditions in obtaining expanded graphite by electrochemical treatment. As described above, the values of DC voltages other than the natural potential were set to 0.6V to It has been found that if the range is 0.8 V and the application time is 48 hours or more, according to the present invention, the angle between the main faces of the graphene facing each other can stably and reliably obtain various expanded graphite. Invented the invention. The voltage application time is more preferably 60 hours or more, and still more preferably 80 hours or more.
すなわち、本発明の膨張化黒鉛は、上記のようにして得られ、ＸＲＤパターンにおいて、２θ（ＣｕＫα）が８度〜１２度の範囲内に位置する回折ピークを有し、２５度〜２７度の範囲内の回折ピーク高さが０カウント以上２００カウント以下である。２θ（ＣｕＫα）が２５度〜２７度の範囲内にある回折ピークは、元の黒鉛の（００２）面によるピークであり、本発明の膨張化黒鉛は、この２５度〜２７度の範囲内の回折ピークが小さいため、元の黒鉛とは構造が異なるものである。また、２θ（ＣｕＫα）が８度〜１２度の範囲内にある回折ピークは、膨張化黒鉛の（００２）面による回折ピークであり、従って、本発明は、グラフェン間に硝酸イオンなどの酸性電解質イオンがインターカレートされている、すなわち層間物質挿入黒鉛である。 That is, the expanded graphite of the present invention is obtained as described above. In the XRD pattern, 2θ (CuKα) has a diffraction peak located in the range of 8 degrees to 12 degrees, and 25 degrees to 27 degrees. The diffraction peak height within the range is 0 to 200 counts. The diffraction peak in which 2θ (CuKα) is in the range of 25 ° to 27 ° is a peak due to the (002) plane of the original graphite, and the expanded graphite of the present invention is in the range of 25 ° to 27 °. Since the diffraction peak is small, the structure is different from the original graphite. In addition, the diffraction peak in which 2θ (CuKα) is in the range of 8 degrees to 12 degrees is a diffraction peak due to the (002) plane of expanded graphite. Therefore, the present invention provides an acidic electrolyte such as nitrate ion between graphenes. Ions are intercalated, that is, intercalated graphite.
本発明の膨張化黒鉛では、上記のような層間物質の挿入により、もとの黒鉛よりもグラフェン間の距離が広げられ、膨張化黒鉛とされている。そして、本発明では、上記８度〜１２度の範囲内に現れる回折ピークの高さ１０カウント以上５００カウント以下の範囲にある。この回折ピークの高さが１０カウント以上５００カウント以下であることは、対向
し合っているグラフェンの主面間の成す角度が様々であることを意味する。すなわち、対向し合っているグラフェンの主面間の角度が様々であるため、上記回折ピークの形がブロードとなっている。
In the expanded graphite of the present invention, the distance between the graphenes is expanded as compared with the original graphite by inserting the interlayer material as described above, and the expanded graphite is obtained. In the present invention, the height of the diffraction peak appearing in the range of 8 degrees to 12 degrees is in the range of 10 counts to 500 counts. That the height of this diffraction peak is 10 counts or more and 500 counts or less means that the angles formed between the main surfaces of the graphene facing each other are various. That is, since the angles between the main surfaces of the graphene facing each other are various, the shape of the diffraction peak is broad.
よって、本発明に係る膨張化黒鉛では、上記硝酸イオンなどがインターカレートされて膨張化黒鉛とされているが、この膨張化黒鉛を形成するグラフェンの主面同士が成す角度が様々であるため、剥離力を加えることにより容易にグラフェンを剥離することができる。より具体的には、対向し合っているグラフェンの主面同士が平行でない場合には、グラフェン積層部分の一方側におけるグラフェン主面間の距離が他方側のグラフェン主面間の距離よりも大きくなる。そのため、剥離力を加えることにより、グラフェンを容易に他方のグラフェンから剥離することができる。 Therefore, in the expanded graphite according to the present invention, the nitrate ions and the like are intercalated into expanded graphite, but the angles formed by the main surfaces of graphene forming the expanded graphite are various. The graphene can be easily peeled off by applying a peeling force. More specifically, when the graphene main surfaces facing each other are not parallel to each other, the distance between the graphene main surfaces on one side of the graphene stack is larger than the distance between the graphene main surfaces on the other side. . Therefore, by applying a peeling force, the graphene can be easily peeled from the other graphene.
よって、本発明に係る膨張化黒鉛を用いることにより、グラフェンや複数枚のグラフェン積層体である薄片化黒鉛を、剥離力を加えることにより容易に得ることができる。 Therefore, by using the expanded graphite according to the present invention, exfoliated graphite that is graphene or a plurality of graphene laminates can be easily obtained by applying a peeling force.
上記膨張化黒鉛からグラフェンまたは薄片化黒鉛を得るための剥離工程については、上記機械的剥離力を加える方法や、超音波などのエネルギーを加える方法などを挙げることができる。剥離方法の一例を説明すると、上記のようにして得られた膨張化黒鉛を適宜の溶媒中に浸漬し、超音波を加える方法を挙げることができる。 Examples of the peeling step for obtaining graphene or exfoliated graphite from the expanded graphite include a method of applying the mechanical peeling force and a method of applying energy such as ultrasonic waves. Explaining an example of the peeling method, there can be mentioned a method in which the expanded graphite obtained as described above is immersed in an appropriate solvent and ultrasonic waves are applied.
上記超音波を加える前の加熱温度としては、溶媒や黒鉛層間に挿入されたイオン種により適正範囲は異なるが、溶媒が水の場合は５℃〜１００℃程度の温度とすればよい。この温度範囲で加熱することにより、グラフェン間の距離をさらに広げることができる。また、上記超音波を加える際に用いる溶媒としては、特に限定されず、水、エタノール、ブタノール、キシレンなどを挙げることができる。 The heating temperature before applying the ultrasonic wave varies depending on the solvent and the ion species inserted between the graphite layers, but when the solvent is water, the heating temperature may be about 5 ° C to 100 ° C. By heating in this temperature range, the distance between graphenes can be further increased. Moreover, it does not specifically limit as a solvent used when applying the said ultrasonic wave, Water, ethanol, a butanol, xylene etc. can be mentioned.
あるいは、本発明により得られた膨張化黒鉛を、必要に応じて層間に挿入されたイオンを除去した後に、樹脂と混練し、混練に際して加えられる剪断力により、膨張化黒鉛を剥離し、グラフェンや薄片化黒鉛としてもよい。この場合には、本発明の膨張化黒鉛から剥離されたグラフェンあるいは薄片化黒鉛が分散された樹脂複合材料を得ることができる。 Alternatively, the expanded graphite obtained according to the present invention is optionally kneaded with a resin after removing the ions inserted between the layers as necessary, and the expanded graphite is peeled off by a shearing force applied during the kneading. It is good also as exfoliated graphite. In this case, a resin composite material in which graphene or exfoliated graphite exfoliated from the expanded graphite of the present invention is dispersed can be obtained.
次に、本発明の具体的な実施例及び比較例を挙げることにより、本発明を明らかにする。 Next, the present invention will be clarified by giving specific examples and comparative examples of the present invention.
（実施例１）
１ｍｍの厚みの黒鉛を作用極として、Ｐｔからなる対照極及びＡｇ／ＡｇＣｌからなる参照極とともに６０重量％濃度の硝酸中に浸漬し、自然電位以外に直流電圧を印加し、電気化学処理を行った。電気化学処理に際しては、０．７Ｖの電圧を１２０時間印加した。このようにして、作用極として用いた黒鉛の結晶構造をＸＲＤにより評価した。電気化学処理により、黒鉛は膨張化黒鉛に変性したことが確認された。図１は膨張化黒鉛のＸＲＤパターンであり、図２はその一部を拡大して示すＸＲＤパターンである。また、図３は、上記のようにして得た膨張化黒鉛を急速加熱して得た黒鉛の走査型電子顕微鏡写真（倍率７０００倍）を示す図である。
Example 1
Using graphite with a thickness of 1 mm as a working electrode, the electrode is immersed in 60 wt% nitric acid together with a reference electrode made of Pt and a reference electrode made of Ag / AgCl, and a direct current voltage is applied in addition to a natural potential to perform an electrochemical treatment. It was. In the electrochemical treatment, a voltage of 0.7 V was applied for 120 hours. Thus, the crystal structure of graphite used as the working electrode was evaluated by XRD. It was confirmed that the graphite was modified into expanded graphite by the electrochemical treatment. FIG. 1 is an XRD pattern of expanded graphite, and FIG. 2 is an XRD pattern showing a part thereof enlarged. FIG. 3 is a view showing a scanning electron micrograph (magnification: 7000 times) of graphite obtained by rapidly heating expanded graphite obtained as described above.
図２から明らかなように、２θ（ＣｕＫα）が２５度〜２７度付近に回折ピークが現れ、ピーク高さは約４０カウントであった。これに対して、２θ（ＣｕＫα）が９度付近に回折ピークが存在していることがわかる。後述の比較例１についての図４に示すＸＲＤパターンでも示されるように、電気化学処理前の黒鉛では、２θ（ＣｕＫα）＝２６度付近に大きな回折ピークが現れる。この回折ピークが、図１ではほとんど消失していることがわかる。 As is clear from FIG. 2, a diffraction peak appeared in the vicinity of 2θ (CuKα) of 25 ° to 27 °, and the peak height was about 40 counts. On the other hand, it can be seen that there is a diffraction peak in the vicinity of 9 degrees of 2θ (CuKα). As shown in the XRD pattern shown in FIG. 4 for Comparative Example 1 described later, a large diffraction peak appears in the vicinity of 2θ (CuKα) = 26 degrees in the graphite before electrochemical treatment. It can be seen that this diffraction peak almost disappears in FIG.
黒丸印を付している２６度付近の回折ピークは、黒鉛の（００２）面に由来する回折ピークであり、図１においてこの回折ピークがほとんど見られないことから、黒鉛のグラフェン間に、硝酸イオンがインターカレートされ、黒鉛の層構造がほぼ消失したと考えられる。なお、■印は膨張化黒鉛のピークを示す。また、９度付近で現れる回折ピークは、グラフェン層間距離が開いている膨張化黒鉛の（００２）面による回折ピークであり、従って、上記処理により硝酸イオンがグラフェン間にインターカレートされていることがわかる。 The diffraction peak near 26 degrees marked with a black circle is a diffraction peak derived from the (002) plane of graphite, and since this diffraction peak is hardly seen in FIG. It is thought that ions were intercalated and the layer structure of graphite almost disappeared. The ■ mark indicates the peak of expanded graphite. Further, the diffraction peak appearing near 9 degrees is a diffraction peak due to the (002) plane of expanded graphite having an open graphene interlayer distance. Therefore, nitrate ions are intercalated between graphenes by the above treatment. I understand.
また、この９度付近の回折ピークは比較的ブロードでピーク高さが低く、そのピーク高さは約４０カウントであった。ピーク高さが低くピークがブロードであることは、グラフェンの主面間の対向している角度がある程度広い分布を有していることを示すと考えられる。従って、実施例で得た膨張化黒鉛では、機械的剥離力や超音波による剥離力を与えることにより容易に剥離し、グラフェンや薄片化黒鉛を得ることができる。 The diffraction peak near 9 degrees was relatively broad and low in peak height, and the peak height was about 40 counts. The fact that the peak height is low and the peak is broad is considered to indicate that the facing angles between the main surfaces of graphene have a distribution that is somewhat wide. Therefore, the expanded graphite obtained in the examples can be easily peeled off by applying a mechanical peeling force or an ultrasonic peeling force to obtain graphene or exfoliated graphite.
後述の図４から明らかなように、元の黒鉛では、２θ（ＣｕＫα）＝２６度付近に非常に大きな回折ピークが現れているのに対し、図１及び図２に示したＸＲＤパターンでは、このような大きな回折ピークは現れていないことがわかる。 As apparent from FIG. 4 described later, in the original graphite, a very large diffraction peak appears in the vicinity of 2θ (CuKα) = 26 degrees, whereas in the XRD pattern shown in FIGS. It can be seen that such a large diffraction peak does not appear.
（実施例２）
電気分解に際しての自然電位以外の直流電圧を０．７Ｖとし、通電時間を４８時間としたことを除いては、実施例１と同様にして膨張化黒鉛を得た。得られた膨張化黒鉛のＸＲＤパターンを図８に示す。
(Example 2)
Expanded graphite was obtained in the same manner as in Example 1 except that the DC voltage other than the natural potential during electrolysis was 0.7 V and the energization time was 48 hours. The XRD pattern of the obtained expanded graphite is shown in FIG.
同じ電圧を印加した実施例１に比べ、通電時間が４８時間と短いが、８〜１２度の範囲に膨張化黒鉛由来の回折ピークが現れ、黒鉛の（００２）面由来の２６度付近の回折ピークも非常に小さいことがわかる。 Compared to Example 1 where the same voltage was applied, the energization time was as short as 48 hours, but a diffraction peak derived from expanded graphite appeared in the range of 8 to 12 degrees, and diffraction near 26 degrees derived from the (002) plane of graphite. It can be seen that the peak is very small.
（比較例１）
比較例１は、実施例１で原材料として用意した通常の黒鉛である。図４は、この元の黒鉛のＸＲＤパターンを示す。元の黒鉛では、２６度付近に非常に大きな回折ピークが現れている。これば、前述した黒鉛の（００２）面による回折ピークである。他方、８度〜１２度の範囲には、回折ピークは現れていない。従って、膨張化黒鉛の（００２）面が存在していないことがわかる。
(Comparative Example 1)
Comparative Example 1 is ordinary graphite prepared as a raw material in Example 1. FIG. 4 shows the XRD pattern of this original graphite. In the original graphite, a very large diffraction peak appears around 26 degrees. This is the diffraction peak due to the (002) plane of graphite described above. On the other hand, no diffraction peak appears in the range of 8 to 12 degrees. Therefore, it can be seen that the (002) plane of expanded graphite does not exist.
（比較例２）
電気分解に際しての自然電位以外の直流電圧を０．７Ｖ、通電時間を２４時間としたことを除いては、実施例１と同様にして膨張化黒鉛を得た。得られた膨張化黒鉛のＸＲＤパターンを図５に示す。
(Comparative Example 2)
Expanded graphite was obtained in the same manner as in Example 1 except that the DC voltage other than the natural potential during electrolysis was 0.7 V and the energization time was 24 hours. The XRD pattern of the obtained expanded graphite is shown in FIG.
図５から明らかなように、２４時間の通電では、２６度付近に現れる回折ピークは約５００カウントと比較的大きかった。他方、８度〜１２度の範囲内に回折ピークが現れており、上記電気化学的処理により硝酸イオンが幾分かインターカレートしていることがわかる。もっとも、前述したように、依然として、２θ（ＣｕＫα）＝２６度付近の回折ピークが比較的大きく、従って、グラフェン間に十分に硝酸イオンがインターカレートされていないことがわかる。 As is apparent from FIG. 5, the diffraction peak appearing near 26 degrees was relatively large at about 500 counts when energized for 24 hours. On the other hand, a diffraction peak appears in the range of 8 degrees to 12 degrees, and it can be seen that nitrate ions are somewhat intercalated by the electrochemical treatment. However, as described above, the diffraction peak in the vicinity of 2θ (CuKα) = 26 degrees is still relatively large. Therefore, it can be seen that nitrate ions are not sufficiently intercalated between the graphenes.
（比較例３）
電気分解に際しての自然電位以外の直流電圧を０．５Ｖ、通電時間を２４時間としたことを除いては、実施例１と同様にして、膨張化黒鉛を得た。得られた膨張化黒鉛のＸＲＤパターンを図６及び図７に示す。
(Comparative Example 3)
Expanded graphite was obtained in the same manner as in Example 1 except that the DC voltage other than the natural potential during electrolysis was 0.5 V and the energization time was 24 hours. The XRD pattern of the obtained expanded graphite is shown in FIGS.
図６から明らかなように、通電時間が２４時間と短いため、２θ（ＣｕＫα）＝２６度付近に回折ピークが比較的大きく現れている。従って、硝酸イオンのインターカレートが十分でないことがわかる。また、膨張化黒鉛の（００２）面由来の回折ピークが８度付近に現れており、この回折ピークの高さが、２６度付近に現れる回折ピークの高さよりも低いため、硝酸イオンのグラフェン間へのインターカレートは比較例２よりも進んでいない。 As is apparent from FIG. 6, since the energization time is as short as 24 hours, a diffraction peak appears relatively large in the vicinity of 2θ (CuKα) = 26 degrees. Therefore, it can be seen that nitrate ions are not sufficiently intercalated. In addition, a diffraction peak derived from the (002) plane of expanded graphite appears near 8 degrees, and the height of this diffraction peak is lower than the height of the diffraction peak near 26 degrees. The intercalation into is not advanced more than Comparative Example 2.
（比較例４）
電気分解に際しての自然電位以外の直流電圧を０．５Ｖ、通電時間を４８時間としたことを除いては、実施例１と同様にして膨張化黒鉛の作製を試みた。得られた膨張化黒鉛のＸＲＤパターンを図９に示す。
(Comparative Example 4)
An attempt was made to produce expanded graphite in the same manner as in Example 1 except that the DC voltage other than the natural potential during electrolysis was 0.5 V and the energization time was 48 hours. The XRD pattern of the obtained expanded graphite is shown in FIG.
図９から明らかなように、２θ（ＣｕＫα）＝２６度付近に回折ピークが現れており、８〜１２度の範囲においても小さな回折ピークが現れている。実施例２に比べれば、直流電圧値を低くしたため、硝酸イオンのインターカレートが進まず、依然として、黒鉛の（００２）面由来の２θ（ＣｕＫα）＝２６度付近の回折ピークが比較的大きいことがわかる。従って、硝酸イオンのインターカレートが十分でないことがわかる。 As is clear from FIG. 9, a diffraction peak appears in the vicinity of 2θ (CuKα) = 26 degrees, and a small diffraction peak also appears in the range of 8 to 12 degrees. Compared with Example 2, since the DC voltage value was lowered, the intercalation of nitrate ions did not proceed, and the diffraction peak near 2θ (CuKα) = 26 degrees derived from the (002) plane of graphite was still relatively large. I understand. Therefore, it can be seen that nitrate ions are not sufficiently intercalated.
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