JP6373771B2 - Method for producing graphene oxide sheet - Google Patents

Description

  The present invention relates to a method for producing a graphene oxide sheet, and particularly relates to a method for producing a graphene oxide sheet using a carbon nanohorn aggregate as a raw material.

Graphene is a sheet-like substance having a thickness of 1 atom, and is formed of a honeycomb-like crystal lattice formed by sp ² bonded carbon atoms. Graphene has excellent properties such as high transparency to light in a wide wavelength range from visible to infrared, and good electrical and thermal conductivity, and has various possibilities including materials for transparent conductive films. Has attracted attention as a material.

  As a method for producing graphene, many methods such as a chemical oxidation peeling method, an epitaxial growth method, and a chemical vapor deposition (CVD) method have been developed one after another. Among them, the CVD method is a main method that can control the preparation of high-quality graphene. On the other hand, in the chemical oxidative peeling method, graphene oxide (hereinafter sometimes referred to as “GO”) is easily made from graphite (Non-Patent Documents 1 to 4), and it is expected to reduce the mass production of graphene. Has been.

  In addition, the obtained GO is highly water-soluble, emits light (fluorescence) in the near-infrared to visible / ultraviolet region, and is rich in oxygen functional groups such as epoxy groups, hydroxyl groups, carbonyl groups, and carboxylic acid groups. Because it has various excellent characteristics such as being easily functionalized, it is also attracting attention for applications in the bio field. Recently, the possibility of application to cell imaging and drug delivery (DDS) using nanographene oxide has been reported (Non-Patent Documents 5 to 7).

  However, the GO sheet obtained by the chemical oxidation delamination method is difficult to control structural features such as size and number of layers because the particle size of the graphite crystal powder as a raw material is not uniform. The size (width, length) of the GO sheet is about 100 nm to several tens of μm. When a GO sheet is applied to the bio / medical field, a small GO of 100 nm or less is required, and therefore it is necessary to further separate and purify it.

Although it is possible to produce a fine GO sheet by subjecting the raw material graphite to an oxidative exfoliation treatment condition such as extending the treatment time or increasing the temperature, there are many structural defects in the produced GO sheet. In addition, it is difficult to control the size (width, length) of the manufactured GO sheet, and various sizes coexist.
Although it is possible to produce a sheet (nanoribbon) having a small width using short carbon nanotubes as a raw material (Non-Patent Documents 8 and 9), only a small amount can be synthesized and it is difficult to adjust the length of the sheet. .

As a method for producing a high-quality GO sheet in large quantities, Patent Document 1 discloses that graphene-containing carbon materials such as graphite and multi-walled carbon nanotubes are dispersed with a dispersing agent such as a surfactant to obtain aggregate units of the graphene-containing carbon materials. It has been proposed to oxidize the graphene-containing carbon material after reducing the size and preferably further removing the large aggregates by centrifugation.
However, in Patent Document 1, the obtained GO sheet is intended to be applied to friction materials, conductive fibers, carbon fibers, high-strength lightweight metal materials, etc., and therefore graphite (graphite). Is used, the shape is flake-like, the length is preferably 10 nm to 500 μm, more preferably 500 nm to 2 μm, and when carbon nanotubes are used, the shape is a band, and the width is It is said that 6 nm to 300 nm is preferable. That is, Patent Document 1 makes no mention of obtaining a small GO sheet having a length of 100 nm or less and a width of 20 nm or less.

On the other hand, in Patent Document 2, a petal-containing carbon nanohorn aggregate is oxidized by heating in hydrogen peroxide, thereby forming a carbon nanohorn aggregate that occupies most of the petal structure.
However, it is intended to obtain a spherical aggregate (aggregate) having a particle size of 50 to 90 nm and apply it to a catalyst carrier, an adsorbent, a dispersant, an ink, a toner, etc., particularly to a catalyst-supported carbon nanohorn aggregate. There is no mention of obtaining a uniform, small-sized sheet.

Hummers, W. S .; Offeman, R. E. Preparation of graphitic oxide. J. Am. Chem. Soc. 1958, 80, 1339. Hirata, M .; Gotou, T .; Horiuchi, S .; Fujiwara, M .; Ohba, M. Thin-film particles of graphite oxide: High-yield synthesis and flexibility of the particles. Carbon 2004, 42, 2929. Dikin, D. A .; Stankovich, S .; Zimney, E. J .; Piner, R. D .; Dommett, G. H. B .; Evmenenko, G .; Nguyen, S. T .; Ruoff, R. S. Preparation and characterization of graphene oxide paper. Nature 2007, 448, 457-460. Li, D .; Mueller, M. B .; Gilge, S .; Kaner, R. B .; Wallace, 2793G. G. Processable aqueous dispersions of graphene nanosheets. Nat. Nanotechol. 2008, 3, 101. Sun, X .; Liu, Z .; Welsher, K .; Robinson, J .; Goodwin, A .; Zaric, S .; Dai. H. Nano-graphene oxide for cellular imaging and drug delivery.Nano Res. 2008, 1, 203. Yang, K .; Zhang, S .; Zhang, G .; Sun, X .; Lee, S .; Liu, Z. Graphene in mice: Ultrahigh in vivo tumor uptake and efficient photothermal therapy.Nano Lett. 2010,10, 3318. Tian, B .; Wang, C .; Zhang, S .; Feng, L .; Liu, Z. Photothermally enhanced photodynamic therapy delivered by nano-graphene oxide. ACS Nano 2011, 5, 7000. Jiao, L .; Zhang, L .; Wang, X .; Diankov, G .; Dai, H. Narrow graphene nanoribbons from carbon nanotubes.Nature 2009, 458, 877-880. Kosynkin, D. V. et al. Longitudinal unzipping of carbon nanotubes to form graphene nanoribbons.Nature 2009, 458, 872-876.

International Publication No. 2011-074125 International Publication No. 2011/093661

  The present invention has been made in view of the current situation, and can be applied to the bio-medical field. The length is 100 nm or less, the width is 20 nm or less, and preferably the length is 50 nm or less. It is an object of the present invention to provide a GO sort manufacturing method capable of producing a small amount of GO sheet having a size of 10 nm or less and having few structural defects in a simple manner and in large quantities.

  The present inventor has made the above object in view of such a current situation, and uses a carbon nanohorn aggregate instead of graphite or carbon nanotube used as a raw material, and undergoes a dispersion step of the aggregate. It was found that GO sheets with uniform nanosize and few structural defects can be synthesized in large quantities by a simple method of oxidation treatment without any problems.

The present invention has been completed based on these findings, and according to the present invention, the following inventions are provided.
[1] A method for producing a graphene oxide sheet, comprising using a carbon nanohorn aggregate as a raw material, subjecting the carbon nanohorn aggregate to an oxidation treatment, and then subjecting to ultrasonic treatment.
[2] The method for producing a graphene oxide sheet according to [1], wherein concentrated oxidation and potassium permanganate are used for the oxidation treatment.
[3] A graphene oxide sheet obtained by the production method according to [1] or [2], wherein the length is 50 nm or less and the width is 10 nm or less.

  According to the present invention, mass production is possible simply. The obtained GO sheet has a length of 50 nm or less, a width of 10 nm or less and a small size, and has few structural defects, so that it can be applied to the medical field. For example, application to electronics etc. is expected by utilizing the characteristics such as excellent conductivity.

4 is an electron micrograph of the fine graphene oxide (S-GO) sheet obtained in Example 1. FIG. The figure which shows the analysis result of the atomic force microscope (AFM) photograph of the S-GO sheet | seat obtained in Example 1, and the thickness (height) of the S-GO sheet | seat. The figure which shows the light absorption spectrum (a) and fluorescence spectrum (b) of the S-GO sheet | seat obtained in Example 1. FIG. The figure which shows the infrared spectroscopy spectrum of the S-GO sheet obtained in Example 1. FIG. It is a figure which shows the result of the thermogravimetric analysis (TGA) of the S-GO sheet | seat obtained in Example 1, a is in oxygen and b is in helium. a is a photograph taken after collecting beads with pG. From the left, photographs of S-GO-IgG, S-GO-BSA, S-GO + IgG, and S-GO. b is a figure which shows the fluorescence spectrum of the liquid eluted from each bead.

The carbon nanohorn has a conical shape with a diameter of 2 to 5 nm and a length of 40 to 50 nm, with the tip of the rolled graphene sheet closed and pointed like a horn. Thus, a spherical aggregate having a diameter of about 100 nm is formed.
The present invention is characterized in that a graphene oxide sheet is obtained by using this carbon nanohorn aggregate as a raw material, subjecting it to an oxidation treatment, and then subjecting it to ultrasonic treatment.

That is, in the present invention, the carbon nanohorn aggregates are oxidized without passing through the aggregate dispersion step as described in Patent Document 1, and the length is 50 nm or less and the width is 10 nm or less. A graphene oxide sheet (GO) can be obtained.
In the present invention, since the shape of the obtained GO sheet is not constant, for convenience, the longer size is referred to as “length” and the shorter maximum value is referred to as “width”.

  In the present invention, the carbon nanohorn aggregate used as a raw material is not particularly limited and can be produced by various means, but by a laser ablation method in which a raw material carbon substance is irradiated with laser light in an inert gas atmosphere. The manufactured products are preferably used because they have the same size (diameter of about 100 nm).

  In the present invention, the oxidation treatment is a known method such as a method of oxidizing using an oxidant such as chlorate, a treatment with concentrated nitric acid and potassium permanganate, which has been used in the conventional chemical oxidative stripping method. It can be done by a method.

In particular, when potassium permanganate is used as the oxidizing agent, it is preferable to add potassium permanganate to a liquid in which carbon nanohorn aggregates are dispersed in concentrated sulfuric acid.
Specifically, for example, potassium permanganate is added at room temperature (20 to 25 ° C.) to a dispersion obtained by stirring carbon nanohorn aggregates in concentrated sulfuric acid for 2 to 24 hours, and then 60 to The mixture is stirred at 80 ° C. for 40 to 60 minutes, and after adding pure water, the reaction is carried out for 30 to 40 minutes.

After the oxidation treatment, the obtained reaction solution is subjected to centrifugation / redispersion of the precipitate until the pH of the supernatant becomes neutral to obtain a precipitate. The obtained precipitate is sonicated by adding water, and then centrifuged to collect centrifugal water. Centrifugal water thus obtained is a transparent dispersion of the micro-sized GO sheet of the present invention.
The ultrasonic treatment conditions in this case are preferably 260 to 300 W and 20 to 60 minutes, and particularly preferably 280 W and 30 minutes.

  The micro GO sheet manufactured by the method of the present invention is a nano-sized sheet having a length of 20 to 100 nm, preferably 20 to 50 nm, a width of 2 to 20 nm, preferably 2 to 10 nm, and a surface area. It is large, has many functional groups, and is highly hydrophilic. Therefore, application to drug delivery (DDS) can be expected as a drug carrier. In particular, because of the uniform and small size, it can be expected that the long residence time in blood, high selective arrival rate to the affected area, discharge to the outside of the body, etc. that are required for practical application to nanocarbon DDS can be improved. .

  Further, the micro GO sheet manufactured in the present invention emits light (fluorescence) in the visible light region, and can be applied to an immunological test as a fluorescent label. In addition, since abundant carboxyl groups and amino groups such as proteins can be linked by amide bonds, functional molecules for biomolecule detection can be added to the surface, which can be applied to bioimaging and biosensors. Application is possible.

  In addition, when the micro GO sheet manufactured by the method of the present invention is reduced by heat treatment, light irradiation or chemical reaction, like a general graphene or graphene oxide, a transparent conductive film, power storage / power generation, transistor integrated circuit, etc. It can also be applied to electronics.

  EXAMPLES Hereinafter, although this invention is demonstrated based on an Example, this invention is not limited to this Example.

Example 1
In this example, a micro GO sheet (hereinafter referred to as “S-GO sheet”) was manufactured as follows.
100 mg carbon nanohorn aggregates (particle diameter 80-100 nm) produced by the laser ablation method are placed in a 100 mL glass bottle, 10 mL concentrated sulfuric acid (98%) is added, and the mixture is stirred for 20 hours at room temperature, and then slowly permanganic acid at room temperature. 100 mg of potassium was added. Thereafter, the glass bottle was stirred at 70 ° C. (water bath) for 1 hour.
Thereafter, the glass bottle is taken out, 50 mL of pure water is added while stirring in an ice bath, and again stirred in a water bath at 70 ° C. for 40 minutes, and hydrogen peroxide (30%, 8 mL) and 12 mL of pure water are added. The reaction was stopped.

Next, the reaction solution was transferred from the glass bottle to a centrifuge tube, centrifuged at 5000 rpm for 1 hour, and the supernatant was discarded. To this centrifuge tube, 10% hydrochloric acid is added to redisperse the precipitate, and then centrifuged at 5000 rpm for 1 hour, and the supernatant is discarded. Further, pure water was added to the centrifuge tube, redispersed and centrifuged (20000 rpm, 20 min), and the supernatant was discarded.
This redispersion / centrifugation operation was repeated 10 times until the pH of the supernatant became neutral.
In this way, 50 mL of pure water was added to the precipitate and subjected to ultrasonic treatment (280 W, 20 minutes), followed by centrifugation (2000 rpm, 20 minutes), and 90% of the centrifuged solution was recovered.
The collected centrifuge was a transparent dispersion of S-GO sheet.

(Example 2)
In this example, the characteristics of the S-GO sheet obtained in Example 1 were examined.
One drop of the dispersion of S-GO obtained in Example 1 was placed on a grid for an electron microscope or a silicon wafer, and the structure and size of the S-GO and the thickness of the S-GO sheet were measured with an electron microscope and an atom. Confirmed with an atomic force microscope.

  FIG. 1 is an electron micrograph of an S-GO sheet. As apparent from FIG. 1, the S-GO sheet had a length of 20 to 50 nm and a width of 2 to 10 nm. This size is almost the same as a single nanohorn.

FIG. 2 is a diagram showing an atomic force microscope (AFM) photograph of the S-GO sheet and its analysis result, and the distance (width) and height in the AB direction at three points 1 to 3 shown in the AFM photograph. The thickness (thickness) is summarized in a table.
As shown in the table, the thickness of the S-GO sheet is 0.7 to 2.1 nm, and it can be seen that a single layer to several layers of graphene sheets coexist.

Fig. 3 shows the light absorption spectrum of the S-GO sheet (Lambda 1050 UV-Vis-NIR spectrophotometer, Perkin-Elmer) (a) and the fluorescence spectrum when excited with light having a wavelength of 345 nm (FluoroLog 3, Horiba) (b ).
As apparent from FIG. 3, the obtained dispersion of S-GO had a broad absorption peak shoulder at 300 nm, and when excited with 345 nm light, strong fluorescence was observed in the wavelength region of 400 to 800 nm.

  Moreover, it was found that the produced S-GO dispersion was freeze-dried, and the yield of S-GO was about 40% from the amount of dried S-GO.

FIG. 4 shows an infrared spectrum (FT-IR) spectrum (Spectrum One, Perkin-Elmer) of the S-GO sheet.
From the results of the FT-IR spectrum, it was found that the S-GO sheet had a functional group such as —OH, —O═O, C—O—C.

FIG. 5 shows the results of thermogravimetric analysis (TGA 2950, TA instruments). For reference, thermogravimetric analysis was also performed on the nanocarbon horn aggregate as a raw material.
In FIG. 5, a is in oxygen for investigating combustion, b is in helium for investigating thermal decomposition, and the solid line indicates the result of the S-GO sheet. What is indicated by a dotted line is the result of the carbon nanohorn aggregate used for reference.
From the figure a, it was found that the combustion temperature of the carbon nanohorn aggregate in oxygen was 600 ° C., whereas the combustion temperature of the S-GO sheet was low and was about 420 ° C. The decrease in weight from room temperature to about 420 ° C. is due to the fact that functional groups such as —OH, —O═O, C—O—C, etc. were oxidized to leave as CO or CO ₂ .
In addition, from FIG. 4b, it can be seen that the carbon nanohorn aggregates are hardly decomposed, whereas the S-GO sheet is decomposed by about 50% at 400 ° C. From this, —OH, —O It was confirmed that the weight of functional groups such as ═O and C—O—C was about 50%.

(Example 3)
As described above, since the S-GO sheet prepared in the present invention has strong visible light fluorescence, it can be applied to an immunological test as a fluorescent label. Moreover, an abundant carboxyl group of the S-GO sheet and an amino group such as a protein can be bonded by an amide bond. Therefore, in this example, application to an immunological test as a fluorescent label was examined as follows.

  About 2 mg of EDC (N, N′-dicyclohexylcarbodiimide) and 2 mg NHS (N-hydroxysuccinimide) were added to the liquid (200 μL, 2 mg / mL) containing S-GO obtained in Example 1, and stirred for 15 minutes. The carboxyl group of S-GO was activated. Thereafter, the activated S-GO dispersion is subjected to ultrafiltration (Mw5000) to remove unreacted NHS and EDC, and the activated S-GO is dispersed in 200 μL of phosphate buffered saline (PBS). S-GO-IgG was synthesized by reacting with 100 μg of immunoglobulin G (Immunoglobulin G: IgG) at room temperature for 2 hours. After the reaction, unreacted IgG was removed by ultrafiltration (Mw300K), and S-GO-IgG was dispersed in PBS and collected.

The obtained S-GO-IgG was mixed with magnetic beads with protein G (pG) (Bio-Adem beads Protein G), S-GO-IgG and pG were coupled, and then, with a magnet, S-GO-IgG was coupled. -IgG / pG magnetic beads were recovered.
Similarly, S-GO-BSA obtained by reacting IgG and BSA (non-antibody protein), a mixture of S-GO and IgG (S-GO + IgG), and only S-GO are also magnets. The beads with pG were recovered.

  FIG. 6a is a photograph of the photograph after collecting the beads with pG. From the left, S-GO-IgG, S-GO-BSA, S-GO + IgG, and S-GO are photographed. Moreover, FIG. 6b is a figure which shows the fluorescence spectrum of the liquid eluted from each bead.

  As is clear from the photograph at the left end of FIG. 6a, S-GO-IgG is completely transparent with the recovery, and the solution that was brown due to S-GO becomes completely transparent, and specifically the target substance Protein G (pG) It was found that the reaction was complete. Then, when the reacted S-GO-IgG-pG was eluted from the beads and the eluate was excited with 345 nm light, fluorescence emission of S-GO could be confirmed (see FIG. 6b).

On the other hand, when only S-GO-BSA obtained by reacting IgG and BSA (non-antibody protein), or a mixture of S-GO and IgG (S-GO + IgG) and S-GO are used, the target substance pG When the beads with pG were recovered with a magnet without coupling, the brown color of the solution due to GO did not change and the fluorescence intensity was very weak.
From this result, S-GO can be expected to be applicable as a fluorescent label for immunoassay.

Claims (3)

Using carbon nanohorn aggregate raw material, after oxidizing process the carbon nanohorn aggregate, sonicated, is 50nm or less in length, oxide graphene sheet width is characterized Rukoto give the following oxide graphene sheet 10nm Manufacturing method.   The method for producing a graphene oxide sheet according to claim 1, wherein concentrated sulfuric acid and potassium permanganate are used for the oxidation treatment. Acid graphene sheet manufacturing method according to claim 1 or 2, wherein the particle diameter of the carbon nanohorn aggregate is 80 to 100 nm.

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