阅读说明：本技术 石墨的薄板状结构物的制造方法、以及薄片化石墨及其制造方法 (Method for producing thin plate-like structure of graphite, and flaked graphite and method for producing same ) 是由 西川泰司 仁科勇太 于 2019-10-31 设计创作，主要内容包括：通过对电化学反应体系流通电流来制造石墨的薄板状结构物,所述电化学反应体系包含：包含石墨的阳极、可以包含石墨的阴极、以及包含四氟硼酸或六氟磷酸作为电解质的电解质溶液。通过对该薄板状结构物施加剥离操作来制造薄片化石墨。(Producing a thin plate-like structure of graphite by passing an electric current through an electrochemical reaction system comprising: an anode comprising graphite, a cathode which may comprise graphite, and an electrolyte solution comprising tetrafluoroboric acid or hexafluorophosphoric acid as an electrolyte. The thin plate-like structure is subjected to a peeling operation to produce flaked graphite.)

1. A method for producing a graphite sheet-like structure, comprising a step of passing an electric current through an electrochemical reaction system, the electrochemical reaction system comprising:

an anode comprising graphite;

a cathode that may comprise graphite; and

an electrolyte solution containing tetrafluoroboric acid or hexafluorophosphoric acid as an electrolyte.

2. The method for producing a graphite sheet-like structure according to claim 1, wherein anions of tetrafluoroboric acid or anions of hexafluorophosphoric acid are intercalated between layers of graphite of the anode to obtain a graphite sheet-like structure.

3. The method for producing a sheet-like structure of graphite according to claim 1 or 2, wherein the graphite-containing anode is obtained by heat-treating a polycondensation polymer compound.

4. The method for producing a sheet-like structure of graphite according to claim 3, wherein the anode comprising graphite is obtained by heat-treating aromatic polyimide.

5. The method for producing a sheet-like structure of graphite according to claim 1 or 2, wherein the graphite-containing anode is obtained by pressurizing expanded graphite obtained by immersing natural graphite in a strong acid and then heating the immersed natural graphite.

6. The method for producing a sheet-like structure of graphite according to any one of claims 1 to 5, wherein the electrolyte solution contains a protic polar solvent or an aprotic polar solvent.

7. The method for producing a sheet-like structure of graphite according to any one of claims 1 to 5, wherein the electrolyte solution contains water and an aprotic polar solvent.

8. The method for producing a sheet-like structure of graphite according to any one of claims 1 to 5, wherein the solvent contained in the electrolyte solution is only water.

9. The method for producing a sheet-like structure of graphite according to any one of claims 1 to 5, wherein the electrolyte solution contains water and a protic polar solvent other than water.

10. The method for producing a sheet-like structure of graphite according to claim 9, wherein the protic polar solvent other than water is an alcohol solvent.

11. A method for producing a graphite sheet-like structure, comprising a step of passing an electric current through an electrochemical reaction system, the electrochemical reaction system comprising:

an anode comprising: graphite obtained by heat-treating a polycondensation polymer compound, or graphite obtained by pressurizing expanded graphite obtained by immersing natural graphite in a strong acid and then heat-treating the immersed natural graphite;

a cathode, which may comprise graphite; and

an electrolyte solution comprising sulfuric acid or nitric acid as an electrolyte.

12. A method of making exfoliated graphite, comprising:

a step of obtaining a graphite sheet-like structure by the production method according to any one of claims 1 to 11; and

and a step of obtaining flaked graphite by applying a peeling operation to the sheet-like structure.

13. The method for producing exfoliated graphite as claimed in claim 12, wherein the peeling operation is an ultrasonic wave irradiation-based peeling operation, a mechanical peeling operation, or a heating-based peeling operation.

14. The method for producing flaked graphite according to claim 12 or 13, wherein the flaked graphite has a thickness of 100nm or less.

15. The method for producing flaked graphite according to any one of claims 12 to 14, wherein the flaked graphite contains oxygen.

16. The method for producing exfoliated graphite as claimed in claim 15, wherein the mass ratio (C/O) of carbon to oxygen of the exfoliated graphite is 20 or less.

17. The method for producing flaked graphite according to claim 15 or 16, wherein the flaked graphite further contains fluorine.

18. A flaked graphite comprising fluorine and oxygen,

the manganese content is 0.002 mass% or less,

the sulfur content is 0.1 mass% or less.

19. The exfoliated graphite as claimed in claim 18, wherein the fluorine content is 0.5% by mass or more and 40% by mass or less, the carbon content is 40% by mass or more and 80% by mass or less, and the oxygen content is 1.0% by mass or more and 50% by mass or less.

20. A flaked graphite which is a flaked graphite comprising oxygen, wherein,

a mass ratio (C/O) of carbon to oxygen of 0.8 to 5,

in a spectrum of Fourier transform infrared spectroscopy (FT-IR), a wavelength of 3420cm^-1The half-value width of the peak in the vicinity was 1000cm^-1The following.

21. The exfoliated graphite as claimed in claim 20, wherein, in the spectrum of Fourier transform infrared spectroscopy, the wavelength is 1720-1740cm^-1The height of the nearby peak is 1590-1620cm relative to the wavelength^-1The ratio of the heights of the nearby peaks is less than 0.3.

22. The exfoliated graphite as claimed in claim 20 or 21, wherein, in a spectrum of X-ray photoelectron spectroscopy (XPS), a ratio of a height of a peak in the vicinity of bond energy 288-289eV to a height of a peak in the vicinity of bond energy 284-285eV is less than 0.05.

23. The exfoliated graphite as claimed in claim 20, wherein, in the spectrum of Fourier transform infrared spectroscopy, the wavelength is 1720-1740cm^-1The height of the nearby peak is 1590-1620cm relative to the wavelength^-1The ratio of the heights of the peaks in the vicinity is 0.3 or more.

24. The exfoliated graphite as claimed in claim 20 or 21, wherein, in a spectrum of X-ray photoelectron spectroscopy (XPS), a ratio of a height of a peak in the vicinity of bond energy 288-289eV to a height of a peak in the vicinity of bond energy 284-285eV is 0.05 or more.

25. A flaked graphite which is a flaked graphite comprising oxygen, wherein,

a mass ratio (C/O) of carbon to oxygen of 0.8 to 5,

in the solid¹³In a C-NMR spectrum, the ratio of the height of a peak at a chemical shift of about 70ppm to the height of a peak at a chemical shift of about 130ppm is 1.0 or less.

26. The flaked graphite of claim 25, wherein in a solid state¹³In the C-NMR spectrum, the ratio of the height of a peak at a chemical shift of 60ppm to the height of a peak at a chemical shift of 70ppm is less than 2.2.

27. The flaked graphite of claim 25, wherein in a solid state¹³In a C-NMR spectrum, the ratio of the height of a peak at a chemical shift of about 60ppm to the height of a peak at a chemical shift of about 70ppm is 2.2 or more.

Technical Field

The present invention relates to a method for producing a graphite sheet-like structure, and flaked graphite and a method for producing the same.

Background

In the description of the present specification, "graphene" refers to a sheet-like substance having a thickness of about one atom and composed of sp 2-bonded carbon atoms. The "sheet-like structure of graphite" is a structure in which an interlayer material is inserted between layers of raw material graphite having a layer structure, and the distance between the layers of graphite (the distance between graphene layers) is increased. The term "exfoliated graphite" refers to a laminate of graphene, which is obtained by applying a peeling operation to the plate-like structure of graphite so that the number of graphene layers is smaller than that of the raw material graphite.

Graphene is a special material having properties such as high carrier mobility, high thermal conductivity, and transparency in one material. In addition, since the structure is an ultimate nano-sheet, it is easy to increase the area of the device, and it is rich in thermal stability and chemical stability, and therefore, it is expected that the nano-carbon material can be applied to advanced industrial materials including the field of electronics.

Graphite is a laminate of a plurality of layers of graphite, and is present in large quantities on the ground. Therefore, since graphite is considered to be a suitable raw material for producing graphene, various attempts have been proposed to produce graphene and/or exfoliated graphite having a much lower number of layers than graphite by exfoliating the layers of the laminate.

As a main method for exfoliating graphite between layers, the following methods are known: a method of applying a mechanical or physical external force thereto; a method of chemically modifying graphite with an oxidant and then performing interlayer peeling; or an electrochemical method in which graphite is used as a working electrode, and the working electrode is immersed in an electrolyte solution to conduct energization, whereby electrolyte ions are intercalated between the graphite layers to obtain a graphite sheet-like structure, and then the sheet-like structure is subjected to interlayer exfoliation.

Typical examples of the method of applying mechanical or physical external force to graphite include a method of peeling off graphite with an adhesive tape (see non-patent document 1) and a method of irradiating with ultrasonic waves for a long time (see non-patent document 2), but these methods are not suitable for mass production because of low operability and yield and low energy efficiency.

A method involving chemical modification of graphite is widely known as a method for producing graphene oxide. However, this method requires a large amount of a powerful oxidizing agent and a harmful substance in the process of exfoliating the graphite interlayer. Therefore, the quality problems such as defects in the chemical structure of the product cannot be avoided. Further, the danger of explosion of the chemical reagents used, the time and labor required to remove them from the product, and the complexity of waste disposal have been hindering the mass production of graphene oxide (see non-patent document 3).

The proposal of embedding electrolyte ions between the layers of the graphite by an electrochemical method and then carrying out interlayer stripping does not need chemical reagents such as an oxidant, a reducing agent and the like. In addition, this method is a scheme of attempting to exfoliate graphite under mild reaction conditions using easily controllable electric energy, implying the possibility of large-scale production of the process.

In this electrochemical method, various attempts have been made to use graphite as a working electrode. Thus, the most widely attempted methods are: an aqueous solution of an acidic substance such as sulfuric acid, nitric acid, or perchloric acid is used as an electrolyte solution, and electric current is applied to the solution to intercalate the acidic substance between the graphite layers serving as a working electrode (anode), followed by exfoliation (see non-patent document 4). Among them, sulfuric acid is a substance frequently used as an electrolyte because it is easily available and an intercalation compound with graphite is easily produced.

However, in the conventional known electrochemical method, defects are easily generated in the structure of the product in the process of the occurrence of the interlayer peeling, and further, the destruction and peeling of the graphite texture structure by the generation of the decomposition gas derived from the electrolyte is a significant obstacle in the expansion of the application of the technology. Further, there is a problem that an undesirable side reaction such as oxidation of water occurs.

In order to avoid these problems, it is attempted to perform intercalation under as mild electrolytic conditions as possible (see patent document 1). However, as a result, it is inevitable to increase the time of the electrochemical treatment, and a complicated electrolytic apparatus or the like for controlling the potential or the like is required, so that the production efficiency is low for large-scale implementation, and the cost is not satisfactory.

In contrast, there is an example in which electrolysis is attempted in a short time. This is an example in which graphene oxide can be synthesized using 50% sulfuric acid water as an electrolyte solution (see non-patent document 5). However, this method requires a step of converting the raw graphite into expanded graphite using concentrated sulfuric acid in a stage prior to the oxidation step, and this step requires a longer time than the oxidation step. In short, it cannot be said that it is a simple method because a two-stage complicated process must be adopted.

On the other hand, for the purpose of avoiding the disadvantages of the electrochemical treatment in the aqueous system, use of a nonaqueous electrolyte has been attempted (see non-patent document 6). Among them, studies on the use of ionic liquids for electrolytes have been actively conducted in recent years, but ionic liquids themselves are extremely expensive and therefore are not suitable for mass production from the viewpoint of economy.

Further, fluorinated graphene oxide is mainly produced by fluorinating graphene oxide obtained by chemically oxidizing graphite. In this chemical oxidation, a large amount of a chemical oxidizing agent such as concentrated sulfuric acid or potassium permanganate is used (see patent documents 2 and 3 and non-patent document 7). Therefore, the obtained graphene oxide contains impurities such as heavy metal components and sulfur components derived from these chemical oxidizing agents. Therefore, it is important that the fluorinated graphene oxide produced by the above method is inevitably contaminated with impurities including a manganese component and a sulfur component. Patent document 3 shows: the fluorinated graphene oxide produced in the examples contains a non-negligible amount of sulfur components.

Further, graphene oxide is known as a compound which is easily reduced. That is, graphene oxide can be easily converted to reduced graphene oxide (rGO) by heating or the action of a reducing agent. Thus, when the graphene oxide is fluorinated, oxygen-containing functional groups such as hydroxyl groups on the skeleton, which are originally contained in the graphene oxide, may be lost to an extent more than necessary. Patent document 3 shows that fluorination of graphene oxide results in loss of the hydroxyl group of graphene oxide.

Further, reduced graphene oxide (rGO) is likely to aggregate and become multilayered, and therefore, it is easily estimated that the monolayer property of the raw material graphene oxide is lost in the fluorination and subsequent isolation processes in the subsequent step, and the graphene oxide becomes multilayered. The evidence is: there is no mention at all in patent documents 2, 3 and non-patent document 7 that the obtained fluorinated graphene oxide maintains the monolayer property.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2012 and 131691

Patent document 2: japanese Kokai publication Hei 2014-504248

Patent document 3: japanese patent laid-open publication No. 2018-76196

Non-patent document

Non-patent document 1: science, 306(5696), 666-9(2004).

Non-patent document 2: small, 6(7), 864-71(2010).

Non-patent document 3: am chem.soc., 80, 1339(1958).

Non-patent document 4: CARBON, 54, 1-21(2013).

Non-patent document 5: nature commun, 9: 145(2018).

Non-patent document 6: adv. funct. mater, 18(10), 1518-25(2008).

Non-patent document 7: j. Mater. chem.A, 2, 8782-8789(2014).

Disclosure of Invention

The invention is toProblems to be solved

As described above, although there are many methods for producing exfoliated graphite by exfoliation of graphite between layers, it is currently difficult to produce exfoliated graphite on a large scale and economically. In order to flexibly apply the flaked graphite as an industrial material, it is required to establish a manufacturing technique which can be economically implemented on a large scale while reducing the environmental load at the time of manufacturing.

In view of the above-described situation, an object of the present invention is to provide a method for efficiently producing a sheet-like structure of high-quality graphite or flaked graphite.

Means for solving the problems

In view of the above problems, the present inventors considered that: in order to put the manufacturing technology of the flaked graphite into practical use, it is the fastest way to improve the electrochemical process into a refining technology. The key point is the invention of an electrolyte as an excellent graphite intercalation material, and intensive studies have been made.

As a result, they found that: the present inventors have completed the present invention by providing an unprecedented excellent graphite intercalation material when tetrafluoroboric acid or hexafluorophosphoric acid is used as an electrolyte.

That is, the first invention relates to a method for producing a graphite sheet-like structure, including a step of passing an electric current to an electrochemical reaction system including: an anode comprising graphite, a cathode which may comprise graphite, and an electrolyte solution comprising tetrafluoroboric acid or hexafluorophosphoric acid as an electrolyte.

According to the first invention, graphite is used as the anode, and an electric current is passed through an electrolyte solution containing tetrafluoroboric acid or hexafluorophosphoric acid as an electrolyte, whereby the graphite can be converted into a graphite sheet-like structure in one stage. The sheet-like structure of graphite of the present invention refers to a product obtained by performing an electrochemical process (i.e., an electrolyzed portion of anode graphite), and the structure does not peel off or separate in an electrolyte solution, but maintains the overall form as an anode. According to the first invention, a thin plate-like structure of graphite in which the distribution of overlapping graphene layers is controlled in the order of nanometers can be suitably produced.

Further, according to the first invention, the above-mentioned electrochemical step is performed alone, and a thin plate-like structure of graphite can be produced in a very short time with high quality and high yield without particularly performing complicated additional treatment such as filtration.

As described above, the electrolyte ions can be highly uniformly and rapidly inserted between graphene layers of graphite constituting the anode. As a result, the obtained graphite sheet-like structure can reduce the number of graphene layers remaining due to insufficient intercalation as much as possible, while having fewer defects in the carbon skeleton structure. Further, from the viewpoints of quality, current efficiency, time efficiency, yield, and low loss including waste, the production efficiency of the graphite sheet-like structure can be dramatically improved.

According to one embodiment of the first invention, the graphite sheet structure can be obtained by intercalating anions of tetrafluoroboric acid or anions of hexafluorophosphoric acid between the graphite layers of the anode. The graphite sheet-like structure obtained here is referred to as a novel expanded graphite structure, and is a structure in which anions of tetrafluoroboric acid or anions of hexafluorophosphoric acid are intercalated between graphite layers, whereby the intervals between graphite layers constituting the graphite are expanded and oxidation is accompanied by a carbon skeleton.

According to one embodiment of the first invention, the anode containing graphite is preferably a material obtained by heat-treating a polycondensation polymer compound, and more preferably a material obtained by heat-treating an aromatic polyimide. Such graphite has a structure in which planar graphite crystal layers are laminated, and is particularly preferable because it is easy to intercalate anions of tetrafluoroboric acid and anions of hexafluorophosphoric acid into the graphite layers, and it is particularly difficult to peel off or detach the graphite from the small pieces during intercalation, and the overall form of the anode is easily maintained. By using such an anode, the effect achieved by the first invention can be further improved.

In addition, according to another embodiment of the first invention, it is also preferable that the anode containing graphite is obtained by high-pressure pressing of expanded graphite obtained by immersing natural graphite in a strong acid and then heat-treating the immersed natural graphite. By using such an anode, the effects achieved by the first invention can also be obtained.

According to a first embodiment of the present invention, the electrolyte solution preferably contains a protic polar solvent or an aprotic polar solvent, and particularly preferably contains water and an aprotic polar solvent. This is expected to help the anions of tetrafluoroboric acid and hexafluorophosphoric acid, which have high lipophilicity, penetrate into the graphite interlayer. Further, since the options of the solvent constituting the electrolyte solution are increased, the range of the electrolysis conditions favorable for efficiently producing the thin plate-like structure of graphite by the first invention is expanded.

According to another embodiment of the first invention, the solvent contained in the electrolyte solution may be only water. Further, the aforementioned electrolyte solution may contain water and a protic polar solvent other than water. The aforementioned protic polar solvent other than water may be an alcohol solvent.

Further, the present inventors found that: when graphite obtained by heat-treating a polycondensation polymer compound or graphite obtained by pressurizing expanded graphite obtained by immersing natural graphite in a strong acid and heat-treating the immersed natural graphite is used as the graphite constituting the anode, a thin plate-like structure of graphite or flaked graphite can be efficiently produced even when sulfuric acid or nitric acid is used as an electrolyte.

That is, according to the second invention, the present invention relates to a method for producing a graphite sheet-like structure, including a step of applying an electric current to an electrochemical reaction system including: an anode comprising graphite obtained by heat-treating a polycondensation polymer compound or expanded graphite obtained by impregnating natural graphite in a strong acid and then heat-treating the impregnated graphite; a cathode that may comprise graphite; and an electrolyte solution containing sulfuric acid or nitric acid as an electrolyte. As in the first invention, the graphite can be converted into a sheet-like structure of graphite in one stage, and the sheet-like structure of graphite can be produced in a very short time with high quality and high yield without particularly performing complicated additional treatment such as filtration.

The third invention relates to a method for producing exfoliated graphite, which comprises: a step of obtaining a graphite sheet-like structure by the first or second production method of the present invention; and a step of obtaining flaked graphite by applying a peeling operation to the thin plate-like structure. Thus, the thin plate-like structure of graphite produced by the first or second invention can be made into a sheet, and thus, a flaked graphite can be produced.

According to a third embodiment of the present invention, the aforementioned peeling operation is preferably an ultrasonic irradiation-based peeling operation, a mechanical peeling operation, or a heating-based peeling operation. This makes it possible to more reliably thin the graphite sheet-like structure.

According to the third invention, it is possible to produce exfoliated graphite having a thickness of 100nm or less.

The flake graphite produced by the third invention preferably contains oxygen, and more preferably has a carbon-to-oxygen mass ratio (C/O) of 20 or less. The flaked graphite preferably further contains fluorine.

According to the third invention, fluorine-containing exfoliated graphite can be produced from graphite without using a chemical oxidizing agent. Therefore, according to the third invention, it is possible to produce a novel fluorine-containing exfoliated graphite which does not substantially contain a heavy metal, particularly a manganese component, and a sulfur component derived from a chemical oxidizing agent.

Further, according to the third invention, when fluorinated graphene oxide is obtained, a step of temporarily separating graphene oxide, which is required in the prior art, is not required, and fluorine-containing exfoliated graphite can be produced without performing such a separation step.

Further, according to the third invention, since the process of separating graphene oxide and fluorinating is not performed, there is no fear that graphene oxide is reduced in the process. That is, oxygen-containing functional groups such as hydroxyl groups of graphene oxide are retained, and as a result, fluorine-containing exfoliated graphite having retained monolayer properties can be produced.

Further, according to the third invention, in addition to the above-described advantages in terms of quality, it is possible to provide a method for producing flaked graphite in which the production efficiency is dramatically improved, from the viewpoint of reducing current efficiency, time efficiency, yield, and loss including waste.

The fourth invention relates to a novel fluorine-containing exfoliated graphite produced by the third invention, and more specifically, to an exfoliated graphite containing fluorine and oxygen and having a manganese content of 0.002 mass% or less and a sulfur content of 0.1 mass% or less.

In a fourth embodiment of the present invention, the exfoliated graphite may be: the fluorine content is 0.5 to 40 mass%, the carbon content is 40 to 80 mass%, and the oxygen content is 1.0 to 50 mass%.

The fifth invention relates to a flaked graphite which is a flaked graphite containing oxygen, wherein the mass ratio (C/O) of carbon to oxygen is 0.8 or more and 5 or less, and the wavelength is 3420cm in a spectrum of Fourier transform infrared spectroscopy (FT-IR)^-1The half-value width of the peak in the vicinity was 1000cm^-1The following.

In a fifth embodiment of the present invention, the above-mentioned exfoliated graphite has a wavelength of 1720-1740cm in a spectrum obtained by Fourier transform infrared spectroscopy^-1The height of the nearby peak is 1590-1620cm relative to the wavelength^-1The ratio of the heights of the peaks in the vicinity may be less than 0.3, and further, in the spectrum of X-ray photoelectron spectroscopy (XPS), the ratio of the height of the peak in the vicinity of the bond energy 288-289eV to the height of the peak in the vicinity of the bond energy 284-285eV may be less than 0.05.

In a fifth other embodiment of the present invention, the above-mentioned exfoliated graphite has a wavelength of 1720-1740cm in a spectrum obtained by Fourier transform infrared spectroscopy^-1The height of the nearby peak is 1590-1620cm relative to the wavelength^-1The ratio of the heights of the peaks in the vicinity may be 0.3 or more, and further,in the spectrum of X-ray photoelectron spectroscopy (XPS), the ratio of the height of the peak in the vicinity of the bond energy 288-289eV to the height of the peak in the vicinity of the bond energy 284-285eV may be 0.05 or more.

The sixth invention relates to exfoliated graphite containing oxygen, wherein the mass ratio (C/O) of carbon to oxygen is 0.8 or more and 5 or less, and the exfoliated graphite is in the form of a solid¹³In a C-NMR spectrum, the ratio of the height of a peak at a chemical shift of about 70ppm to the height of a peak at a chemical shift of about 130ppm is 1.0 or less.

In a sixth embodiment of the present invention, the exfoliated graphite is in a solid state¹³In a C-NMR spectrum, the ratio of the height of a peak at a chemical shift of about 60ppm to the height of a peak at a chemical shift of about 70ppm is less than 2.2, and in other embodiments, the ratio of the height of a peak at a chemical shift of about 60ppm to the height of a peak at a chemical shift of about 70ppm of the exfoliated graphite is 2.2 or more.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, a high-quality graphite sheet-like structure or flake graphite can be efficiently produced.

Drawings

Fig. 1 is a photograph of the appearance of the graphite sheet-like structure, which is the anode immediately after the reaction in example 1.

Fig. 2 is a spectrum based on EDX analysis showing the presence ratio of elements contained in the flake graphite obtained in example 1.

Fig. 3 is a histogram based on SEM analysis showing the particle size of the exfoliated graphite obtained in example 1.

Fig. 4 is an SEM image obtained by photographing the flake graphite obtained in example 1.

Fig. 5 shows the results of AFM analysis of the minimum thickness of the exfoliated graphite obtained in example 1.

Fig. 6 is a photograph of the appearance of the anode immediately after the end of the reaction in example 12.

Fig. 7 is a photograph of the appearance of the anode immediately after the completion of the reaction in example 13.

FIG. 8 shows a graphite foil (EGO) obtained by electrolysis using an aqueous tetrafluoroborate solution^W) And a graphite foil (EGO) electrolyzed using a methanol/aqueous solution of tetrafluoroboric acid^M) The obtained photograph was taken for appearance.

FIG. 9 shows the process of producing EGO^W(i in the figure), EGO^M(ii in the figure) and EGO^S(electrolytic reaction using aqueous sulfuric acid solution; iii) in the figure) by Linear Sweep Voltammetry (LSV).

FIG. 10 (a), (b) and (c) shows EGO^WAnd (3) a graph showing the relationship between the time and current density at the time of electrolysis in the synthesis and the concentration of tetrafluoroboric acid and the C/O ratio of the product. FIG. 10 (d) shows EGO^MGraph of the concentration of tetrafluoroboric acid during synthesis versus the C/O of the product.

FIG. 11 is an EGO^M、EGO^WAnd a spectrum obtained by measuring CGO (based on chemically synthesized graphene oxide) by X-ray photoelectron spectroscopy.

In FIG. 12 a) is EGO^M、EGO^WAnd XRD spectrum of CGO. B) of FIG. 12 is EGO^M、EGO^WLambert-Beer coefficients for CGO and high oxidation CGO (hcgo). C) in FIG. 12 is graphite, EGO^M、EGO^WAnd the results of raman spectroscopic analysis of CGO. D) in FIG. 12 is EGO^M、EGO^WAnd the results of FT-IR analysis of CGO. E) of FIG. 12 is EGO^M、EGO^WAnd CGO solid¹³Results of C-NMR. F) of FIG. 12 is EGO^M、EGO^WAnd TGA-MS of CGO.

FIG. 13 (a) is an EGO^WSEM photograph of (a). FIG. 13 (b) is an EGO^MSEM photograph of (a). FIG. 13 (c) is an EGO^WAFM photograph of (1). FIG. 13 (d) is an EGO^MAFM photograph of (1). In FIG. 13, (e), (f) and (g) are each CGO and EGO^WAnd EGO^MDispersed in water and photographed after 2 months. In FIG. 13, (h), (i) and (j) are CGO and EGO, respectively^WAnd EGO^MDispersed in methanol and the resulting photograph taken after 1 week.

FIG. 14 (a) is for EGO after reduction (thermal reduction t or chemical reduction hy)^M、EGO^WAnd CGO. FIG. 14 (b) is an XPS C1s spectrum. Fig. 14 (c) shows the result of the interlayer distance. Fig. 14 (d) shows the result of XPS atomic composition.

FIG. 15 is a graph for EGO after reduction (chemical reduction hy or thermal reduction t)^M、EGO^WAnd CGO.

Fig. 16 a) shows the measurement results of the capacity of a lithium ion battery using graphite or CGO, EGOW, or EGOM after thermal reduction as an electrode active material. Fig. 16 b) shows the removal rate of dye molecules when EGOM, EGOW and CGO were used as a filtration membrane.

Detailed Description

Hereinafter, specific embodiments of the present invention will be described in detail.

The present invention converts graphite used as an anode into a graphite sheet-like structure by an electrochemical reaction using a specific electrolyte.

In the present invention, the anode is made of a conductive material containing layered graphite, and the graphite is not particularly limited as long as it forms (intercalates) an intercalation compound with the electrolyte according to the present invention, and can be selected from a wide range of materials. Examples thereof include natural graphite, synthetic graphite, graphite obtained by heat-treating a polycondensation polymer compound, and Highly Oriented Pyrolytic Graphite (HOPG).

The polycondensation polymer compound is not particularly limited, and examples thereof include aromatic polyimide, aromatic polyamide, polyoxadiazole, polyphenylene ethylene, and the like. Among them, aromatic polyimide is preferable.

As a suitable example of the graphite, graphite obtained by heat-treating an aromatic polyimide is exemplified. Such graphite has a structure in which planar graphite crystal layers are laminated, and particularly, intercalation of anions of tetrafluoroboric acid or anions of hexafluorophosphoric acid into the graphite interlayer is easy to occur, and in addition, exfoliation, separation, and the like of the graphite from the small pieces particularly hardly occur when intercalation is performed, and the overall form as an anode is easily maintained. Therefore, a sheet-like structure of graphite or flaked graphite of higher quality can be produced more efficiently.

The anode may be formed by high-pressure pressing of expanded graphite obtained by immersing natural graphite in a strong acid such as concentrated sulfuric acid or nitric acid and then subjecting the graphite to a heat treatment process in an expansion furnace. By using the graphite powder as an anode, a high-quality graphite sheet-like structure or a graphite flake can be efficiently produced.

The shape of the anode is not particularly limited, and an appropriate shape can be appropriately selected from a wide variety of options such as a rod shape, a plate shape, a block shape, a sheet shape, a foil shape, and a roll shape.

The cathode used in the method for producing a graphite sheet-like structure of the present invention is an electrode forming a pair with the anode, but does not directly participate in the production of the graphite sheet-like structure. Therefore, the cathode is not particularly limited as long as it has a function of providing electrons to cations generated as a result of an anode reaction and can construct an electrochemically stable system, and can be appropriately selected from a wide range of materials. For example, the metal material may be selected from metals such as platinum, graphite, stainless steel, copper, zinc, and lead, or carbonaceous materials. The shape of the cathode may be appropriately selected from a wire-like, plate-like, and mesh (mesh) cathode.

When gas is generated in the cathode reaction, the area of the cathode may be increased to the extent possible so as not to impair the efficiency of the cathode reaction or to increase the resistance of the electrolytic system without an end.

In the production method of the present invention, an ion exchange membrane, a spacer, or the like may be provided between the anode and the cathode in order to prevent an undesired reaction from occurring in the anode and/or the cathode, or to prevent a short circuit between the anode and the cathode.

The electrode system in the production method of the present invention may be composed of only the anode and the cathode, and in the case of performing more precise potential control, a reference electrode may be further used in addition to the anode and the cathode. As the reference electrode, an electrode prepared by a conventional method such as Ag/AgCl can be used.

In the present invention, as the electrolyte, tetrafluoroboric acid or hexafluorophosphoric acid is used. The two may be used in combination. These anions are very rapidly intercalated into the graphite interlayer, and therefore, the current efficiency and the time efficiency in the electrochemical reaction are extremely high, and a high-quality graphite sheet-like structure can be efficiently produced. The tetrafluoroboric acid or hexafluorophosphoric acid may be obtained in a pure form, or may be used in the form of a 40 to 50% aqueous solution, or may be diluted with an appropriate solvent if necessary.

The electrolyte solution is obtained by dissolving the above electrolyte in a solvent. As the solvent that can be used, one that is miscible with tetrafluoroboric acid, hexafluorophosphoric acid or an aqueous solution thereof and that is electrochemically stable in the production of the sheet-like structure of graphite can be appropriately selected.

Preferred solvents are protic polar solvents such as water, lower alcohols such as methanol, ethanol, and propanol; aprotic polar solvents such as acetonitrile, dimethylformamide, dimethoxyethane, dimethyl carbonate, propylene carbonate, and dimethyl sulfoxide. Of these, 1 species may be used, or 2 or more species may be used in combination.

As the solvent, water is preferably contained. As the solvent, only water may be used, and in addition, the solvent may contain water and a protic polar solvent other than water, and further, water and an aprotic polar solvent may also be contained. The flaked graphite obtained by using a solvent containing water has the advantage of having good affinity with water and excellent dispersibility in water. Further, by using water and a protic or aprotic polar solvent other than water, it is expected that the anions of tetrafluoroboric acid and hexafluorophosphoric acid having high lipophilicity will be assisted in the graphite intercalation. Further, since the options of the solvent constituting the electrolyte solution are increased, the range of electrolysis conditions favorable for efficiently producing a graphite thin plate-like structure is expanded.

Further, when an alcohol solvent, which is a protic polar solvent, is used as a solvent of the electrolyte solution, the resulting thin plate-like structure of graphite or flaked graphite may have an alkoxy group and/or an alkyl group derived from the used alcohol solvent. The flaked graphite obtained by using an alcohol solvent has an advantage of good affinity with the alcohol solvent and excellent dispersibility in the alcohol solvent.

The concentration of the electrolyte in the electrolyte solution may be such that the resistance of the electrochemical reaction system is sufficiently low, and anions of tetrafluoroboric acid or anions of hexafluorophosphoric acid are rapidly supplied to the graphite of the anode to obtain a thin plate-like structure of graphite. Preferably 1.0 to 50 mass%, and more preferably 5.0 to 50 mass%.

In the present invention, a direct current voltage is applied to an electrochemical reaction system composed of the anode, the cathode, and the electrolyte solution. The voltage to be applied may be applied so long as at least a potential necessary for intercalation of anions of tetrafluoroboric acid or hexafluorophosphoric acid into the graphite interlayer of the anode can be secured, and an overvoltage may be applied in order to rapidly obtain a thin plate-like structure of graphite. The practical applied voltage is preferably set so as to exceed voltage drop factors governed by the resistance of the electrolytic system, such as the electrolyte concentration, the solvent composition of the electrolyte solution, the distance between the anode and the cathode, and the electrolysis temperature. Specifically, the voltage is preferably applied in a range of 1.5 to 50V, and more preferably in a range of 2.0 to 25V.

The density of the current supplied to the anode is controlled by the applied voltage and the surface area of the electrode. According to the present invention, when tetrafluoroboric acid or hexafluorophosphoric acid is used as an electrolyte, anions thereof are extremely rapidly intercalated between graphite layers, and graphene layers can be uniformly expanded. Therefore, the current density can be set widely from the region of small density to the region of high density, and a graphite sheet-like structure can be obtained regardless of the magnitude of the current density. Preferably 1 to 2000mA/cm²More preferably 10 to 1000mA/cm²。

In one embodiment of the present invention, it is also preferable to set the current supplied to the electrochemical reaction system to a constant value. In this case, the preferred set current value is set so as to fall within the preferred current density range. In this case, although the voltage applied to the electrochemical reaction system may vary depending on the degree of progress of the reaction and the resistance value of the system, the preferred range of the applied voltage is the same as the above-described range of the applied voltage.

The amount of electricity (F/mol, F: Faraday constant) supplied to the electrochemical reaction system is preferably 0.2F/mol or more, more preferably 0.8 to 3.0F/mol, and still more preferably 1.0 to 2.0F/mol, based on the number of moles of carbon atoms in the graphite supplied to the electrolytic reaction. When the amount of electricity is supplied, a thin plate-like structure of graphite and flaked graphite can be efficiently obtained.

The temperature of the electrolyte solution when a voltage is applied to the electrochemical reaction system may vary depending on the kind of solvent in which the electrolyte is dissolved and the concentration of the electrolyte solution, and practically, the lower limit is a temperature at which the electrolyte solution does not freeze, and the upper limit is a boiling point of the electrolyte solution. The method can be preferably carried out at 0 to 100 ℃. It is more preferable to carry out the reaction at 0 to 80 ℃.

In the present invention, tetrafluoroboric acid or hexafluorophosphoric acid as an electrolyte is theoretically not consumed before and after the reaction. Therefore, the electrolyte solution after use in the production of the graphite sheet-like structure can be repeatedly reused. In this case, the reaction system may be replenished with an electrolyte reduced by a thin plate-like structure or the like attached to graphite taken out from the electrolyte solution, as necessary.

Further, the thin plate-like structure of graphite immediately after the reaction according to the present invention is sandwiched and adhered by the electrolyte solution containing tetrafluoroboric acid or hexafluorophosphoric acid. The electrolyte solution component associated with the graphite sheet-like structure can be recovered. The larger the scale of production of the graphite sheet-like structure, the more effective the recovery. Specific examples of the recovery method include a method in which a sheet-like structure of graphite containing an electrolyte solution is placed in a centrifugal separator, a method in which the sheet-like structure is subjected to pressure filtration, and a method in which an electrolyte solution is continuously separated by a belt press (backing press).

The graphite sheet-like structure taken out of the electrolyte solution may be washed with an excess amount of deionized water until the washing solution becomes neutral, regardless of whether the recovery process is performed, to thereby remove the electrolyte solution component from the structure.

The sheet-like structure of graphite obtained by the above steps may be subjected to the subsequent production step of exfoliated graphite in a wet state, or may be subjected to the production step of exfoliated graphite after being subjected to a drying step as necessary. The specific drying method is not particularly limited, and for example, drying may be carried out at a temperature of 80 ℃ or lower using a constant temperature dryer or a vacuum dryer.

In the present invention, as described above, by applying a current to an electrochemical reaction system using an anode comprising graphite and an electrolyte solution containing tetrafluoroboric acid or hexafluorophosphoric acid as an electrolyte, anions of tetrafluoroboric acid or anions of hexafluorophosphoric acid are rapidly and uniformly intercalated between the layers of graphite, and as a result, a graphite sheet-like structure in which the interlayer distance between the individual graphenes constituting graphite is uniformly extended can be obtained.

According to another aspect of the method for producing a sheet-like structure of graphite of the present invention, when an anode comprising graphite obtained by heat-treating a polycondensation polymer compound or graphite obtained by pressurizing expanded graphite obtained by immersing natural graphite in a strong acid and then heat-treating the impregnated natural graphite is used as an electrolyte, sulfuric acid or nitric acid can be used. In this case, a high-quality graphite sheet-like structure or flake graphite can be efficiently produced. In this embodiment, an aqueous sulfuric acid solution may be used as the electrolyte solution. The concentration of the aqueous sulfuric acid solution is not particularly limited, and may be, for example, 1 to 60 wt%. Other conditions are based on the conditions described above for the scheme using tetrafluoroboric acid or hexafluorophosphoric acid as electrolyte.

By applying a peeling operation to the graphite sheet-like structure obtained by the present invention, it is possible to suitably obtain flaked graphite having a thickness of 100nm or less.

The peeling operation is not particularly limited, and examples thereof include a peeling operation by ultrasonic irradiation, a peeling operation by applying a mechanical peeling force, a peeling operation by heating, and the like. More specifically, it can be exemplified that: dispersing a graphite sheet-like structure in an appropriate amount of deionized water, and applying an ultrasonic irradiation device thereto; a method of treating with a mixer or a device capable of applying a shearing force, and the like. The treated product after the exfoliation operation may be freeze-dried, or a cake obtained by filtration or centrifugal separation may be subjected to the same drying treatment as that performed for the above-described sheet-like structure of graphite.

From the above, it is possible to advantageously obtain exfoliated graphite having a thickness of 100nm or less. The thickness of the exfoliated graphite is more preferably 50nm or less, and still more preferably 10nm or less. In particular, exfoliated graphite having a thickness of 1nm or less is preferable. The average particle size of the exfoliated graphite may vary within a range of nanometers to millimeters, but is preferably 30nm or more and 1mm or less, more preferably 50nm or more and 100 μm or less, and still more preferably 100nm or more and 50 μm or less. The obtained flaked graphite is preferably composed of graphene oxide (graphene containing oxygen). In the graphene oxide, the mass ratio (C/O) of carbon to oxygen is preferably 20 or less, more preferably 15 or less, further preferably 10 or less, further preferably 5 or less, and particularly preferably 3 or less. The exfoliated graphite is more preferably composed of fluorinated graphene oxide (graphene containing fluorine and oxygen).

The fluorine-containing exfoliated graphite suitably produced by the present invention has a high purity and a low impurity content because of the characteristics of the production method of the present invention. In particular, it is characterized by a small content of heavy metal components and sulfur components. Specifically, in the fluorine-containing exfoliated graphite, the manganese content is preferably 0.002 mass% or less and the sulfur content is preferably 0.1 mass% or less, and more preferably the manganese content is 0.001 mass% or less and the sulfur content is 0.01 mass% or less.

Further, the fluorine-containing exfoliated graphite preferably has a fluorine content of 0.5% by mass or more and 40% by mass or less, a carbon content of 40% by mass or more and 80% by mass or less, and an oxygen content of 1.0% by mass or more and 50% by mass or less; more preferably, the fluorine content is 1.0 mass% or more and 15 mass% or less, the carbon content is 45 mass% or more and 75 mass% or less, and the oxygen content is 15 mass% or more and 45 mass% or less.

The oxygen-containing exfoliated graphite suitably produced by the present invention has a carbon-to-oxygen mass ratio (C/O) of 0.8 to 5 inclusive and a wavelength of 3420cm in a spectrum of Fourier transform infrared spectroscopy (FT-IR)^-1The half-value width of the peak in the vicinity is preferably 1000cm^-1The following. The half width is more preferably 700cm^-1Hereinafter, more preferably 500cm^-1Below, particularly preferably 400cm^-1The following. The mass ratio (C/O) of carbon to oxygen is preferably 0.9 or more and 3 or less, more preferably 0.9 or more and 2 or less, and still more preferably 0.9 or more and 1.5 or less.

In one embodiment of the foregoing oxygen-containing exfoliated graphite, the wavelength of 1720-1740cm in the spectrum of Fourier transform infrared spectroscopy^-1The height of the nearby peak is 1590-1620cm relative to the wavelength^-1The ratio of the heights of the nearby peaks is preferably less than 0.3. More preferably 0.25 or less, and still more preferably 0.2 or less. In this embodiment, further, in the spectrum of X-ray photoelectron spectroscopy (XPS), the ratio of the height of the peak in the vicinity of the bond energy 288-289eV to the height of the peak in the vicinity of the bond energy 284-285eV is preferably less than 0.05. More preferably 0.04 or less, and still more preferably 0.03 or less. The exfoliated graphite according to this embodiment has good affinity with water and excellent dispersibility in water, and can be suitably produced by using only water as a solvent for an electrolyte solution in a method for producing a sheet-like structure of graphite.

In other embodiments of the foregoing oxygen-containing exfoliated graphite, the wavelength of 1720-1740cm in the spectrum of Fourier transform infrared spectroscopy^-1The height of the nearby peak is 1590-1620cm relative to the wavelength^-1The ratio of the heights of the peaks in the vicinity is preferably 0.3 or more. More preferably 0.4 or more, and still more preferably 0.5 or more. In this embodiment, further, in the spectrum of X-ray photoelectron spectroscopy (XPS), the ratio of the height of the peak in the vicinity of the bond energy 288-289eV to the height of the peak in the vicinity of the bond energy 284-285eV is preferably 0.05 toThe above. More preferably 0.06 or more, and still more preferably 0.07 or more. The exfoliated graphite according to this embodiment has good affinity with an alcohol solvent and excellent dispersibility in an alcohol solvent, and can be suitably produced by using an alcohol solvent as a solvent for an electrolyte solution in a method for producing a sheet-like structure of graphite.

In the oxygen-containing exfoliated graphite suitably produced by the present invention, the mass ratio (C/O) of carbon to oxygen is 0.8 or more and 5 or less, and the graphite is in a solid state¹³In the C-NMR spectrum, the ratio of the height of a peak at a chemical shift of about 70ppm to the height of a peak at a chemical shift of about 130ppm is preferably 1.0 or less. The ratio is more preferably 0.8 or less, still more preferably 0.6 or less, and particularly preferably 0.5 or less. The mass ratio (C/O) of carbon to oxygen is preferably 0.9 or more and 3 or less, more preferably 0.9 or more and 2 or less, and still more preferably 0.9 or more and 1.5 or less.

In one embodiment of the foregoing oxygen-containing exfoliated graphite, the solid is¹³In the C-NMR spectrum, the ratio of the height of a peak at a chemical shift of about 60ppm to the height of a peak at a chemical shift of about 70ppm is preferably less than 2.2. More preferably 1.9 or less, and still more preferably 1.7 or less. The exfoliated graphite according to this embodiment has good affinity with water and excellent dispersibility in water, and can be suitably produced by using only water as a solvent for an electrolyte solution in a method for producing a sheet-like structure of graphite.

In other embodiments of the foregoing oxygen-containing exfoliated graphite, the solid is¹³In the C-NMR spectrum, the ratio of the height of a peak at a chemical shift of about 60ppm to the height of a peak at a chemical shift of about 70ppm is preferably 2.2 or more. More preferably 2.5 or more, and still more preferably 2.8 or more. The exfoliated graphite according to this embodiment has good affinity with an alcohol solvent and excellent dispersibility in an alcohol solvent, and can be suitably produced by using an alcohol solvent as a solvent for an electrolyte solution in a method for producing a sheet-like structure of graphite.

Examples

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

< method for measuring the carbon-to-oxygen mass ratio (C/O) of flaked graphite >

The mass ratio of carbon to oxygen (C/O) of the graphite flakes was measured by the principle of Energy dispersive X-ray analysis (EDX). The specific determination method comprises the following steps: the dried powder of flaked graphite obtained by the predetermined treatment was uniformly adhered to a carbon tape and measured by JSM IT-100 manufactured by japan electronics.

< method for measuring average particle diameter and maximum particle diameter of flaked graphite >

The average particle diameter and the maximum particle diameter of the exfoliated graphite were measured using a Scanning Electron Microscope (SEM). Specifically, a thin dispersion of exfoliated graphite was applied to a silicon substrate, and measured at an acceleration voltage of 30kV using S-5200 manufactured by Hitachi to obtain an SEM image. The average particle diameter was calculated as follows: a certain number (for example, 200) of particles are picked up at random on the SEM image, the particle diameter of each particle is measured, and the total value thereof is divided by the number of particles. The maximum particle size is the maximum particle size observed on the SEM image.

< method for measuring minimum thickness of flaked graphite >

The minimum thickness of the exfoliated graphite was determined using an Atomic Force Microscope (AFM). Specifically, the thin dispersion of exfoliated graphite was applied to a mica substrate, and measured by tapping mode using SPM-9700HT manufactured by shimadzu corporation.

< method for measuring manganese and Sulfur contents in flaked graphite >

The manganese and sulfur content of the flaked graphite was determined using Inductively Coupled Plasma Mass Spectrometry (ICP-MS, Inductively Coupled Plasma-Mass Spectrometry). Specifically, a thin dispersion of flaked graphite was analyzed at 7700c, manufactured by Agilent.

(example 1)

A glass reactor was prepared, and 100ml of a 5% aqueous solution of tetrafluoroboric acid was added as an electrolyte solution. Will be used as anodeA commercially available graphite foil (foil obtained by heat-treating and graphitizing aromatic polyimide which is a polycondensation polymer compound, manufactured by KANEKA Co., Ltd.) was used in an area of 15cm²(65 mg in terms of graphite) was fixed in the solution so as to be immersed in the electrolyte, and a platinum wire electrode was provided as a cathode. This was connected to a DC power supply, and electrolysis was carried out at room temperature for 10 minutes at a constant current of 0.7A. In this process, a smooth increase in the thickness of the graphite foil and a brownish appearance of the surface were observed in the portion of the anode immersed in the electrolyte. Fig. 1 shows a photograph taken of the anode immediately after the reaction was completed. The anode after the reaction hardly peeled off or fell off in the electrolyte, and the entire sheet shape was maintained, but the thickness of the portion immersed in the electrolyte was significantly increased compared to that before the reaction. It can be confirmed that: anions of tetrafluoroboric acid are rapidly intercalated into the graphite foil, and as a result, a thin plate-like structure of graphite is formed.

The graphite foil after the reaction was taken out from the electrolyte, and washed with deionized water until the washing solution became neutral, to obtain an undried blackish brown graphite sheet structure. After a small amount of deionized water was added thereto, ultrasonic irradiation was performed for 15 minutes, followed by freeze-drying, whereby 110mg of flaked graphite was obtained. According to the results of EDX analysis, this graphite was composed of flaked graphite containing 3 mass% of fluorine and oxygen atoms at a carbon to oxygen mass ratio (C/O) of 1.10 (fig. 2). According to the results of SEM analysis, the average particle size was 450nm (FIG. 3), and the maximum particle size was 10 μm (FIG. 4). Also, according to the result of AFM analysis, the minimum thickness was 1.0nm (FIG. 5). Further, according to the result of ICP analysis, the content of manganese was 0.1ppm or less, and the content of sulfur was 0.1ppm or less.

(example 2)

Electrolytic reaction and post-treatment were carried out under the same conditions as in example 1 except that 100ml of a 50% aqueous solution of tetrafluoroboric acid was used as an electrolytic solution, thereby obtaining 124mg of exfoliated graphite. According to the results of the analysis, the graphite was composed of a flake graphite containing oxygen atoms at a ratio of carbon to oxygen mass ratio (C/O) of 0.98 and containing 8 mass% of fluorine, and had an average particle diameter of 150nm, a maximum particle diameter of 50 μm and a minimum thickness of 0.8 nm. Further, according to the result of ICP analysis, the content of manganese was 0.1ppm or less, and the content of sulfur was 0.1ppm or less.

(example 3)

Electrolytic reaction and post-treatment were carried out under the same conditions as in example 1 except that electrolysis was carried out for 10 minutes at a constant current under energization conditions of 1.0A, thereby obtaining 154mg of graphite flake. According to the results of the analysis, the graphite was composed of flaked graphite containing oxygen atoms at a ratio of carbon to oxygen mass ratio (C/O) of 1.00 and containing 8 mass% of fluorine. Further, according to the result of ICP analysis, the content of manganese was 0.1ppm or less, and the content of sulfur was 0.1ppm or less.

(example 4)

Electrolytic reaction and post-treatment were carried out under the same conditions as in example 1 except that 100ml of a 20% aqueous solution of hexafluorophosphoric acid was used as an electrolytic solution, thereby obtaining 100mg of flaked graphite. According to the results of elemental analysis, the graphite was composed of flaked graphite containing oxygen atoms at a carbon to oxygen mass ratio (C/O) of 1.25 and containing 2 mass% of fluorine, and had an average particle diameter of 140nm, a maximum particle diameter of 35 μm and a minimum thickness of 0.8 nm. Further, according to the result of ICP analysis, the content of manganese was 0.1ppm or less, and the content of sulfur was 0.1ppm or less.

(example 5)

40ml of a 50% aqueous solution of tetrafluoroboric acid was prepared, and ethanol was added thereto in such a manner that the volume thereof became 100 ml. An electrolytic reaction and a post-treatment were carried out under the same conditions as in example 1 except that this was used as an electrolytic solution, thereby obtaining flaked graphite 85 mg. According to the results of elemental analysis, this graphite was composed of a flake graphite containing oxygen atoms at a ratio of carbon to oxygen mass ratio (C/O) of 1.50 and containing 10 mass% of fluorine. Further, according to the result of ICP analysis, the content of manganese was 0.1ppm or less, and the content of sulfur was 0.1ppm or less.

(examples 6 to 8)

An electrolytic reaction and a post-treatment were carried out under the same conditions as in example 5 except that the ethanol was changed to the aprotic polar solvent described in table 1-1, thereby obtaining exfoliated graphite. The amounts of flaked graphite obtained, the mass ratio of carbon to oxygen (C/O), the fluorine content, the manganese content, and the sulfur content in each example are shown in Table 1-1.

[ tables 1-1]

(example 9)

As an electrolyte, 40ml of a 5% aqueous solution of tetrafluoroboric acid was added. A commercially available sheet (PF-HP manufactured by Toyo carbon Co., Ltd.) obtained by pressurizing expanded graphite as an anode under high pressure was partially impregnated (the area of the impregnated portion was 1 cm)²150mg in terms of graphite) was fixed in the solution so as to be immersed in the electrolyte, and a platinum wire electrode was provided as a cathode. This was connected to a DC power supply, and electrolysis was carried out at room temperature for 10 minutes at a constant current of 0.7A. The anode after the end of the reaction retained the shape of the sheet, but the thickness of the portion immersed in the electrolyte was significantly increased compared to that before the reaction. The anode was subjected to post-treatment under the same conditions as in example 1, whereby 192mg of exfoliated graphite was obtained. According to the results of the analysis, the graphite was composed of flaked graphite containing oxygen atoms at a ratio of carbon to oxygen mass ratio (C/O) of 3.20 and containing 1.5 mass% of fluorine. Further, according to the result of ICP analysis, the manganese content was 0.1ppm or less, and the sulfur content was 4 ppm.

(example 10)

As an electrolytic solution, 40ml of a 5% aqueous solution of tetrafluoroboric acid was prepared. A general isotropic graphite sheet as an anode was divided into a portion (the area of the impregnated portion was 1 cm)²125mg in terms of graphite) was fixed in the solution so as to be immersed in the electrolyte, and a platinum wire electrode was provided as a cathode. This was connected to a DC power supply, and after electrolysis was performed at room temperature for 10 minutes at a constant current of 0.7A, post-treatment was performed under the same conditions as in example 1, whereby 95mg of exfoliated graphite was obtained. According to the analysis result, the graphite contains oxygen atoms in a ratio of 3.80 mass ratio (C/O) of carbon to oxygen and 1 mass% of fluorine, an average particle size of 180nm, a maximum particle size of 55 μm and a minimum thickness of 0.8 nm. Further, according to the result of ICP analysis, the manganese content was 0.1ppm or less, and the sulfur content was 0.03 mass% (300 ppm).

(example 11)

Electrolytic reaction and post-treatment were carried out under the same conditions as in example 1 except that the energization time was changed to 5 minutes, whereby 82mg of exfoliated graphite was obtained. According to the results of the analysis, the graphite was composed of flaked graphite containing oxygen atoms at a ratio of carbon to oxygen mass ratio (C/O) of 3.00 and containing 2 mass% of fluorine. Further, according to the result of ICP analysis, the content of manganese was 0.1ppm or less, and the content of sulfur was 0.1ppm or less.

(example 12)

An electrolytic reaction was carried out under the same conditions as in example 1 except that 100ml of a 50% sulfuric acid aqueous solution was used as an electrolytic solution. In this process, no smooth increase in the thickness of the graphite foil was observed in the anode, and a phenomenon was visually observed in which significant bubbles were generated from the anode surface and the black granular small pieces were peeled off and dropped in the electrolyte. Fig. 6 shows a photograph of the anode immediately after the completion of the reaction. From this result, it was confirmed that: the sulfuric acid electrolyte used in example 12 was too slowly inserted into the graphite layers as compared with the electrolyte used in example 1, and a thin plate-like structure of graphite was preferentially formed, and electric energy was concentrated on the surface and the edge of the anode, thereby inducing decomposition of water and the electrolyte. The results can be presumed to be: the secondary generation of gaseous components originating from oxygen and sulfur drastically causes the disintegration of the structure of the graphite surface.

The graphite foil after the reaction was taken out from the electrolyte, washed with deionized water until the washing solution became neutral, and then freeze-dried, whereby 36mg of a black half cake was obtained. According to the analysis result, the mass ratio (C/O) of carbon to oxygen in the graphite was a ratio of 13.60.

From the above results it is clear that: in the case of producing a thin plate-like structure of graphite or flaked graphite by an electrochemical reaction, the first invention using tetrafluoroboric acid or hexafluorophosphoric acid as an electrolyte is overwhelmingly superior to the case of using sulfuric acid as an electrolyte in terms of industrial utility values such as current efficiency, time efficiency, and quality.

(example 13)

An electrolytic reaction was carried out under the same conditions as in example 1, except that 100ml of a 60% nitric acid aqueous solution was used as an electrolytic solution. In this process, a smooth increase in the thickness of the graphite foil was hardly observed in the anode, and from the beginning of the reaction, it was confirmed that a significant bubble was generated on the anode surface and the edge portion thereof was slightly expanded, but a significant change in appearance was not observed in most of the anode. Fig. 7 shows a photograph of the anode immediately after the completion of the reaction. From this result, it is presumed that the electrolyte of nitric acid used in example 13 is too slowly inserted into the graphite layers as compared with the electrolyte used in example 1, and electric energy is concentrated on the surface and the edge of the anode, thereby causing decomposition of water and the electrolyte: in the anode, the portion in contact with the electrolyte remains largely in the state of the raw material graphite, while the edge portion slightly expands.

The graphite foil after the reaction was taken out from the electrolytic solution, washed with deionized water until the washing solution became neutral, and then freeze-dried, whereby 5.7mg of a black powder was obtained from the edge portion of the anode. According to the analysis results, the graphite had a carbon to oxygen mass ratio (C/O) ratio of 7.80.

From the above results it is clear that: in the case of producing a thin plate-like structure of graphite or flaked graphite by an electrochemical reaction, the first invention using tetrafluoroboric acid or hexafluorophosphoric acid as an electrolyte is overwhelmingly superior to the case of using nitric acid as an electrolyte in terms of industrial utility values such as current efficiency, time efficiency, and quality.

Comparative example 1

The electrolytic reaction was carried out under the same conditions as in example 12, except that a general isotropic graphite sheet was used as the anode. The reacted isotropic graphite flakes were taken out from the electrolyte, washed with deionized water until the washing solution became neutral, and then freeze-dried, thereby obtaining black half cakes. According to the results of the analysis, the mass ratio (C/O) of carbon to oxygen in the graphite exceeded 20. From the results, it is found that: in example 12, graphite having a high oxygen content can be obtained as compared with comparative example 1.

Comparative example 2

The electrolytic reaction was carried out under the same conditions as in example 13, except that a general isotropic graphite sheet was used as the anode. The reacted isotropic graphite flakes were taken out from the electrolyte, washed with deionized water until the washing solution became neutral, and then freeze-dried, thereby obtaining black half cakes. According to the results of the analysis, the mass ratio (C/O) of carbon to oxygen in the graphite exceeded 20. From the results, it is found that: in example 13, graphite having a high oxygen content was obtained as compared with comparative example 2.

[ tables 1-2]

(examples 14 to 16)

As the anode, a commercially available graphite foil (foil obtained by heat-treating and graphitizing aromatic polyimide which is a polycondensation polymer compound manufactured by KANEKA corporation) (5cm × 4cm × 20 μm) was used, and as the cathode, a platinum wire electrode was used, and as the electrolyte, a 20% tetrafluoroboric acid aqueous solution (water 80%), a 20% tetrafluoroboric acid methanol/aqueous solution (water 30%, methanol 50%), or a 20% sulfuric acid aqueous solution (water 80%) was used. Each electrode was connected to a DC power supply and was operated at a constant current density (180mA · cm) at room temperature^-2) And electrolysis was carried out for 6 minutes with the cut-off voltage set to 14V.

In this process, the graphite foil was not broken and the thickness increased from 20 μm to 8mm, 400 times, in the system using tetrafluoroboric acid as the electrolyte. Fig. 8 shows the appearance of the graphite foil after electrolysis in a system in which tetrafluoroboric acid was used as the electrolyte. On the other hand, in a system using sulfuric acid as an electrolyte, exfoliation and destruction of the graphite layer occur.

And (3) recovering the reacted graphite foil by filtering, and washing the graphite foil by using deionized water until the washing liquid is neutral to obtain the graphite sheet-shaped structure. After dispersing the graphite in water, ultrasonic wave irradiation was performed for 30 minutes, followed by freeze drying for 48 hours, thereby obtaining exfoliated graphite.

Hereinafter, a sheet-like structure or a flaked graphite of graphite obtained using a 20% tetrafluoroboric acid aqueous solution as an electrolyte solution is referred to as EGO^WExample 14, a sheet-like structure or a flaked graphite of graphite obtained using a 20% methanol tetrafluoroborate/water solution was designated as EGO^MExample 15A thin plate-like structure of graphite or a flaked graphite obtained by using a 20% sulfuric acid aqueous solution was referred to as EGO^S(example 16).

(LSV)

In the system for producing each EGO, Linear Sweep Voltammetry (LSV) was performed under the same conditions as described above. The results are shown in FIG. 9. EGO^WThe LSV curve of (a) in fig. 9 represents four consecutive reaction processes. Namely, ionization of graphite at 0.3 to 1.6V, intercalation at 1.7V, functionalization at 2.2 to 2.7V, and gas generation at 2.7V and beyond.

EGO^MLSV curve (fig. 9 (ii)), ionization and intercalation voltage vs EGO^WThe same applies to the case of the above, but the voltage range for functionalization is widened to 2.0 to 3.0V, and the gas generation is suppressed until the voltage range is 3.0V.

In contrast, EGO^SThe LSV curve of (iii) in fig. 9 shows only 3 reaction stages. Namely, ionization at 0.5 to 1.5V, intercalation at 1.6V, and gas generation at 2.0V and beyond. The absence of functionalization reactions reflects the fact that: HSO₄ ^-The dissociation of ions into the gas competes with their intercalation, and the graphite layer is destroyed before complete oxidation.

EGO^MAnd EGO^WIn this way, the synthesis of flake graphite by non-destructive intercalation is realized, and thereby an unexpected phenomenon occurs, i.e., oxidation of the graphite foil outside the electrolytic solution. First, intercalation and functionalization are performed for 0 to 5 minutes. Intercalation occurs in the graphite in the electrolyte, and the thickness increases immediately. Finally, is thickThe increase in the degree proceeds to the upper part of the graphite foil outside the electrolyte. The reason for this is that, during intercalation and functionalization, the graphite layer performs capillary absorption of the electrolyte, in the EGO^SThis phenomenon was not observed.

(influence of electrolytic time, Current Density, concentration)

Next, CHN elemental analysis was performed to evaluate the degree of functionalization of EGO produced under various electrolysis conditions, and the mass ratio of carbon to oxygen (C/O) was evaluated.

Regarding EGO at constant current^WAs shown in FIG. 10 (a), the influence of the time during the synthesis was that the C/O decreased from 2.85 to 1.46 when the electrolysis time was increased from 5 minutes to 10 minutes. However, even if the electrolysis time is further prolonged, the oxidation does not progress further.

With regard to EGO^WThe current density during the synthesis was changed from 6 to 90mA cm as shown in FIG. 10 (b)^-2While, C/O decreased from 6.14 to 1.38. The current density exceeds 180mA cm^-2No significant improvement was observed. To increase EGO^WThe desired current density is 180mA cm^-2。

With regard to EGO^WAs shown in FIG. 10 (C), the best result of the effect of the tetrafluoroboric acid concentration during the synthesis was that the C/O ratio was 0.99 when the tetrafluoroboric acid concentration was 42%. As the water content in the electrolyte increases, the C/O also increases. This can be achieved by embedded BF₄ ^-The decrease in ion content and the increase in gas generation due to water decomposition were described.

As shown in FIG. 10 (d), in EGO^MThe same tendency was observed in (1), and when the concentration of tetrafluoroboric acid was increased, C/O was decreased. However, when the tetrafluoroboric acid concentration is 10%, EGO is present^WMedium C/O is 1.82, EGO^MMedium is 1.42. This suggests that: methanol suppresses the generation of gas and the destruction of graphite foil, and realizes uniform and complete functionalization.

The samples used below were produced under optimal conditions. I.e. for EGO^WTetrafluoroboric acid 42% and water 58% are the best electrolytes, so thatThe sample made with it is called EGO^W-42%. Furthermore, for EGO^MThe best electrolyte was tetrafluoroboric acid 20%, water 30%, and methanol 50%, and the sample prepared using this was called EGO^M-20％。

Comparative example preparation of CGO

3.0g of flake (flake) -shaped natural graphite was added to 75mL of 95% sulfuric acid, and KMnO was added slowly while keeping the temperature below 10 ℃₄9.0 g. The resulting mixture was stirred at 35 ℃ for 2 hours. While the resulting mixture was vigorously stirred, it was diluted with 75mL of water while cooling so that the temperature did not exceed 50 ℃. The resulting suspension was further treated with 30% H₂O₂7.5mL of the aqueous solution was treated. And purifying the obtained graphite oxide suspension by using water and centrifugal separation until the graphite oxide suspension is neutral, and freeze-drying to obtain the CGO.

High oxidation CGO (hcgo) was manufactured by using CGO instead of natural graphite and performing the above steps.

(XPS)

X-ray photoelectron spectroscopy (XPS) was used to ascertain the atomic composition of the sample surface immediately after fabrication. XPS was measured using JPS-9030 with pulse energy set at 20 eV. The results are shown in fig. 11 and table 2. A C-1s peak and an O-1s peak were observed in all samples, and a small F-1s peak was also observed in each EGO sample. EGO^W42% oxygen content 34.2% by weight, carbon to oxygen mass ratio (C/O) 1.8, EGO^M20% oxygen content 35.2% by weight, C/O1.7. On the other hand, the oxygen content of CGO was 40.5 wt%.

In addition, in EGO^MAnd CGO, peaks near 288-^WThis peak was not observed. With respect to the ratio of the height of the peak in the vicinity of the bond energy 288-289eV to the height of the peak in the vicinity of the bond energy 284-285eV, in EGO^MMedium is 0.09 in EGO^WIs 0 in (1).

[ Table 2]

	CGO	EGOW-42％	EGOM-20％
				C(at％)	63.4	69.6	68.1
O(at％)	34.8	28.4	29.4
				S(at％)	1.8	-	-
F(at％)	-	2	2.5

(XRD)

A) of FIG. 12 shows an EGO^W-42％、EGO^MXRD patterns of 20% and CGO (comparative). XRD uses 2 theta range (range) set to 5-75 ° and Cu Ka radiationThe assay was performed with the PANalytical Co.X' part PRO. As a result, EGO^MThe same spectrum is shown for CGO, but in EGO^WIn (3), the GO (002) diffraction peak shifts, appearing at higher angles. The result represents EGO^WHas a sheet distance smaller than EGO^MAnd CGO.

B) of fig. 12 shows the Lambert-Beer coefficient at 660 nm. In the figure, the value obtained by dividing the absorbance at 660nm measured by a JASCOV-670 spectrophotometer by the length of the cuvette is plotted. EGO^W42% coefficient of 109.0, EGO^MCoefficient 586.5 for 20%, coefficient 65.9 for CGO, and coefficient 39.7Lg for highly oxidized CGO (HCGO)^-1m^-1. From the results, it is found that: the conjugated electronic structure in EGO is less destroyed than CGO, EGO^MWith EGO^WCompared with a continuous conjugated electronic structure.

C) of fig. 12 shows the result of raman spectroscopy. Raman spectra were determined using Horiba Jobin Yvon Inc.T-64000. The graphite foil before electrolysis had lengths of 1578 cm and 2714cm corresponding to the G band and the 2D band^-1Has a strong peak at the center, but after electrolysis, it is 1360cm corresponding to D band^-1A new peak is generated.

D) of fig. 12 shows the result of the FT-IR analysis. FT-IR was measured using SHIMADZU IR Tracer 100. O-H stretching vibration (3420 cm) was observed in each sample^-1) C ═ O stretching vibration (1720) 1740cm^-1) C-C stretching vibration (1590-1620 cm)^-1) C-O vibration (1250-^-1) Such same spectrum. On the basis of the EGO^MOf-20%, methoxy (2976, 1467, 1056 cm)^-1) Showing a characteristic frequency band.

In EGO^M-20% and EGO^WOf-42%, O-H stretching vibration (3420 cm) compared to CGO^-1) The peak of (a) is sharp. Regarding the half-value width of the peak, EGO^M334cm in-20%^-1、EGO^W257cm in 42%^-1In CGO, 1115cm^-1。

In addition, in EGO^M-20% of middle, with EGO^WC ═ O stretching vibration (1720) 1740cm compared to-42%^-1) The peak of (a) appears larger. 1740cm with respect to wavelength 1720^-1The height of the nearby peak is 1590-1620cm relative to the wavelength^-1Ratio of heights of nearby peaks, EGO^M0.58 in-20%, EGO^W0.19 in 42%.

E) of FIG. 12 shows a solid¹³Results of C-NMR. Solid body¹³C-NMR was measured using an NMR system (11.7T magnet, DD2 spectrometer; Agilent technology Inc.) with a magic angle rotation (MAS) set at 10 kHz. The presence of epoxy (60ppm), hydroxyl (72ppm) and carboxyl (168ppm) was confirmed in each EGO, and the EGO was treated with^MIn-20%, the presence of an alkyl group (16ppm), a fluoro group (85ppm), an alkoxide group (60ppm) is further indicated.

In CGO, the peak of hydroxyl group (72ppm) appeared large, while in EGO, it appeared that^M-20% and EGO^WIn-42%, the peak was hardly observed. That is, the ratio of the height of a peak at a chemical shift of about 70ppm to the height of a peak at a chemical shift of about 130ppm was 1.3 in CGO, while EGO was^M0.43 in-20%, EGO^W0.38 in 42%.

In addition, in EGO^WIn 42%, the peak of epoxy or alkoxide groups (60ppm) is less than that of EGO^M-20%. That is, regarding the ratio of the height of a peak in the vicinity of chemical shift 60ppm to the height of a peak in the vicinity of chemical shift 70ppm, EGO^W42% of the total is 1.5 EGO^M3.1 in-20%.

The functional groups that GO has can be removed by heat treatment. CGO generally releases carbon monoxide, carbon dioxide and water at 130-200 ℃. F) of fig. 12 shows the TGA-MS results for each GO. TGA was performed using RIGAKU TG 8121. According to the results of TGA-MS, EGO^W42% hydrogen fluoride, EGO, at 200 ℃ and 320 ℃^M20% of the hydrogen fluoride and methane are released at 200 ℃ and 320 ℃. These results demonstrate EGO^W-42% comprising fluorine, EGO^M-20% comprises fluorine and comprises methoxy and/or methyl groups.

Fig. 13 (a) and (b) show the results of a Scanning Electron Microscope (SEM). In SEM measurement, each EGO was deposited on SiO₂On a/Si substrate. About the device composed ofDistribution of longitudinal dimension calculated by more than 100 EGO pieces in EGO^W0.45. + -. 0.03 μm (0.04-1.78 μm) in 42% of EGO^M0.12. + -. 0.01 μm (0.031-0.363 μm) in-20%.

FIGS. 13 (c) and (d) show the results of an atomic force microscope (AFM; SHIMADZU SPM-9700 HT). In the AFM measurements, each EGO was deposited on mica by spin coating. Analysis of more than 100 flakes of EGO, regarding the average thickness of each flake, EGO^W42% of the total residues are 1.36nm EGO^M1.27nm in-20%. Furthermore, it can be seen that: in EGO^WOf 42%, 62% or more of the flakes are a monolayer(s) (ii)<1.5nm), more than 95 percent of the total weight is single-layer to two-layer (2 nm); in EGO^MOf 20%, 88% or more of the flakes are a monolayer (<1.5nm) and 97% or more of the total amount of the polymer particles is a single layer to two layers (about 2 nm).

Fig. 13 (e) to (j) show the evaluation results of the dispersibility of each EGO and CGO immediately after completion of the preparation. Freeze-dried GO at 0.33mgmL^-1Is dispersed in water or methanol. All showed good dispersibility in water and exhibited nematic liquid crystal properties for at least 2 months (fig. 13 (e) - (g), photographs taken after 2 months). In contrast, in methanol, EGO^W42% and CGO aggregated after 1 week (FIGS. 13 (h) and (i), photographs taken of the state after 1 week), EGO only^M20% remained dispersed after 1 week (fig. 13 (j), photograph taken after 1 week). Known EGO^MThe affinity of-20% to methanol is high.

(characteristics after reduction)

The EGO and CGO are subjected to chemical reduction and thermal reduction. In the chemical reduction, GO just after the completion of the production was dispersed in water, and hydrazine 0.4mLg was added^-1Thereafter, the resulting solution was heated at 90 ℃ for 2 hours. Thermal reduction was performed by maintaining at 220 ℃ for 2 hours, followed by 600 ℃ for 1 hour in a furnace. In each case, the obtained substance was further dispersed in water, filtered with filter paper, and then compressed to prepare a plate (pallet). EGO to be reduced by hydrazine^W、EGO^MAnd CGO are respectively called hyEGO^W、hyEGO^MAnd hyCGO, thermally reduced EGO^W、EGO^MAnd CGOOtherwise known as tEGO^W、tEGO^MAnd tCGO.

Fig. 14 (a), (b), (C), and (d) show the results of XRD, XPS C1s, interlayer distance, and XPS atomic composition measured for each GO after reduction. With respect to XRD, higher shifts in diffraction angles occur in any reduced GO. This is caused by the removal of the functional group on the graphene surface, and it can be confirmed from the XPS result.

Fig. 15 shows the results of the conductivity measured by the four-terminal method for each reduced GO. From the results, it is found that: the thermal reduction has a higher conductivity-improving effect and the EGO has^MThe effect of (2) is particularly high.

(use as negative electrode of lithium ion Battery)

Each tGO was further used as an active material in the negative electrode of a lithium ion battery.

First, each EGO or CGO is placed in N₂Heating at 650 deg.C under atmosphere to obtain tEGO or tCGO. The negative electrode was prepared using these teego, tCGO or graphite as an active material, acetylene black as a conductive material and polyvinylidene fluoride as a binder at a weight ratio of 7:2:1, and further using N-methyl-2-pyrrolidone as a solvent and a copper foil as a current collecting plate.

As the positive electrode, a CR2032 coin cell was assembled using metal lithium with Whatman1823-257 as a separator. The electrolyte was 1M L dissolved in a mixture of Ethylene Carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 3:7^-1LiPF₆。

For the obtained lithium ion Battery, a potential window is set to 0.01-3V, and a multi-channel Battery tester (5808 channel Battery Cycler) is used for performing a charge-discharge cycle test. The results are shown in a) of fig. 16. tEGO^W、tEGO^MAnd tCGO both showed the same performance over graphite. The charging rate is 372mAg^-1The capacity at that time was 495, 554, 513mAhg^-1The charging rate is 7440mAg^-1The capacity at that time was 163, 195, 176mAhg^-1。

(use as filtration Membrane)

In order to effectively utilize the two-dimensional morphology of EGO, thin films of EGO are produced according to the following procedure. First, each GO powder was dispersed in deionized water at 0.1mg/mL, and subjected to centrifugation twice at 6000rpm for 5 minutes to remove precipitates. 6mL of the resulting GO solution was filtered using a polycarbonate membrane and allowed to dry at room temperature for 1 day to obtain a thin film.

For these films, at 35kgfcm^-2And a flow rate of 0.1mLmin^-1Evaluation of dye molecule under the conditions of (methyl orange 10. mu. gmL)^-1) The removability of (2). The result is shown in b) of fig. 16. In EGO^W88% of methyl orange molecules were removed from the films made in-42%, in EGO^MThe films made in-20% removed 97% of the methyl orange molecules. The results were comparable to the performance of the films produced in CGO.