Method for preparing large graphene sheets in large scale

Abstract

A method for preparing large graphene sheets in large scale includes steps of: under a mild condition, processing graphite powders with intercalation through an acid and an oxidant; washing away metal ions and inorganic ions in the graphite powders with dilute hydrochloric acid, then filtering and drying; and, finally processing with a heat treatment. The present invention breaks through a series of bottlenecks restricting an efficient preparation of graphene that result from a traditional method of using large amounts of deionized water to wash graphite oxide to be neutral, and easily realizes a batch production. A radial scale of the prepared graphene sheets is distributed from 20 um to 200 um.

Claims

1. A method for preparing large graphene sheets in large scale, comprising steps of: under a mild condition, processing graphite powders with intercalation through an acid and an oxidant; washing away metal ions and inorganic ions in the graphite powders with dilute hydrochloric acid, then filtering and drying; and, after a heat treatment, obtaining the large graphene sheets.

2. The method for preparing the large graphene sheets in large scale, as recited in claim 1, wherein the acid comprises at least one member selected from a group consisting of concentrated sulphuric acid, concentrated nitric acid, phosphoric acid and perchloric acid.

3. The method for preparing the large graphene sheets in large scale, as recited in claim 1, wherein the oxidant comprises at least one member selected from a group consisting of potassium permanganate, potassium chlorate, sodium chlorate, potassium persulfate and potassium dichromate.

4. The method for preparing the large graphene sheets in large scale, as recited in claim 1, wherein the graphite powders comprise at least one member selected from a group consisting of natural flake graphite powders, expandable graphite powders and expanded graphite powders.

5. The method for preparing the large graphene sheets in large scale, as recited in claim 1, wherein an appropriate acid amount for each gram of the graphite powders is 20-60 ml and an appropriate oxidant amount for each gram of the graphite powders is 5-10 g.

6. The method for preparing the large graphene sheets in large scale, as recited in claim 1, wherein an appropriate amount of the dilute hydrochloric acid for each gram of the graphite powders is 150-350 ml and a volume percentage concentration of the dilute hydrochloric acid is 0.5-10%.

7. The method for preparing the large graphene sheets in large scale, as recited in claim 1, wherein a temperature of the heat treatment is 500-1,350° C.

8. The method for preparing the large graphene sheets in large scale, as recited in claim 1, wherein a radial scale of the large graphene sheets is distributed from 20 μm to 200 μm.

9. A method for preparing large graphene sheets in large scale, comprising steps of: (A) mixing graphite powders with an acid; slowly adding an oxidant in an ice bath; mixing evenly and reacting in the ice bath for 2-48 hours; rising a temperature to 35° C., and continuing oxidizing for 36-120 hours; diluting with water, adding hydrogen peroxide, and obtaining a mixed aqueous solution containing graphite oxide; (B) processing the mixed aqueous solution containing the graphite oxide with vacuum filtration, and obtaining filter cakes; washing with dilute hydrochloric acid having a volume concentration of 10%, and then washing with dilute hydrochloric acid having a volume concentration of 0.5-1% to wash off remaining metal ions and inorganic ions; filtering, and drying; and (C) grinding the filter cakes and processing with the heat treatment for 15-30 seconds, and finally obtaining the large graphene sheets.

10. The method for preparing the large graphene sheets in large scale, as recited in claim 9, wherein: in the step (A), an appropriate amount of the hydrogen peroxide for each gram of the graphite powders is 2-20 ml and an appropriate water amount for each gram of the graphite powders is 150-200 ml.

11. The method for preparing the large graphene sheets in large scale, as recited in claim 9, wherein in the step (B), a drying temperature is 30-85° C., and a drying time is 48-200 hours; and, in the step (C), a grinding equipment is an edge runner, a vibration mill, a turbine grinder, a jet mill, a fan mill, a sand mill, a colloid mill, a ball mill or a family-use grinder.

12. A method for preparing large graphene sheets in large scale, comprising steps of: under a mild condition, processing graphite powders with intercalation through an acid and an oxidant; washing away metal ions and inorganic ions in the graphite powders with dilute hydrochloric acid, then filtering and drying; and, after a heat treatment, obtaining the large graphene sheets; wherein: the acid comprises at least one member selected from a group consisting of concentrated sulphuric acid, concentrated nitric acid, phosphoric acid and perchloric acid; the oxidant comprises at least one member selected from a group consisting of potassium permanganate, potassium chlorate, sodium chlorate, potassium persulfate and potassium dichromate; the graphite powders comprise at least one member selected from a group consisting of natural flake graphite powders, expandable graphite powders and expanded graphite powders; an appropriate acid amount for each gram of the graphite powders is 20-60 ml and an appropriate oxidant amount for each gram of the graphite powders is 5-10 g; an appropriate amount of the dilute hydrochloric acid for each gram of the graphite powders is 150-350 ml and a volume percentage concentration of the dilute hydrochloric acid is 0.5-10%; a temperature of the heat treatment is 500-1,350° C.; and a radial scale of the large graphene sheets is distributed from 20 μm to 200 μm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Other features, objects, and advantages of the present invention will become more apparent from reading the detailed description of non-limiting embodiments with reference to the following figures.

[0028] FIG. 1 is a process flow diagram of a method for preparing graphene according to the present invention.

[0029] FIG. 2 is X-ray diffraction spectra of graphite, graphite oxide and graphene according to a first preferred embodiment of the present invention.

[0030] FIG. 3 is a scanning electron microscope (SEM) photo of the graphene according to the first preferred embodiment of the present invention.

[0031] FIG. 4 is a local transmission electron microscope (TEM) photo of graphene sheets according to the first preferred embodiment of the present invention.

[0032] FIG. 5 is Raman spectra of graphene, graphite oxide and graphite powders according to a second preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0033] The present invention is illustrated in detail with figures and preferred embodiments. The following embodiments will help those skilled in the art better understand the present invention, and not in any way limit the present invention. It shall be noted that several variants and improvements can be made without departing from concept of the present invention for those of ordinary skill in the art. All these fall within the protection scope of the present invention.

[0034] The present invention relates to a method for preparing large graphene sheets in large scale, comprising steps of: processing large graphite sheets with intercalation and modification through an acid and an oxidant; washing away metal ions and inorganic ions in the graphite powders with dilute hydrochloric acid, filtering, and drying; and, after a heat treatment, obtaining the high-quality large graphene sheets. The method effectively avoids a series of problems restricting an efficient preparation of high-quality graphene arising from washing graphite oxide to be neutral with water in conventional methods. The present invention specifically comprises following steps of:

[0035] (1) mixing graphite with the acid; slowly adding the oxidant in an ice bath; evenly mixing, and reacting in the ice bath for 2-48 hours; rising a temperature to 35° C., and continuing oxidizing for 36-120 hours; diluting with water, adding a certain amount of hydrogen peroxide, and obtaining a mixed aqueous solution containing graphite oxide; wherein: the graphite comprises at least one member selected from a group consisting of natural flake graphite, expandable graphite and expanded graphite, and a sheet size of the graphite is optimal from 300 μm to 500 μm; the acid (generally recognized as an acid of 98% concentration) comprises at least one member selected from a group consisting of concentrated sulphuric acid, concentrated nitric acid, phosphoric acid and perchloric acid; the oxidant comprises at least one member selected from a group consisting of potassium permanganate, potassium chlorate, sodium chlorate, potassium persulfate and potassium dichromate; a proportion of the graphite to the acid is 1 g: 20-60 ml, a proportion of the graphite to the oxidant is 1 g: 5-10 g, and a proportion of the graphite to a 20% (V/V) aqueous hydrogen peroxide solution is 1 g: 2-20 ml;

[0036] (2) processing the mixed aqueous solution containing the graphite oxide with vacuum filtration, and obtaining graphite oxide filter cakes; washing with 10% aqueous hydrochloric acid solution, washing off remaining metal ions and inorganic ions and filtering, and drying at a certain temperature; wherein: a proportion of the graphite oxide to the dilute hydrochloric acid is 1 g: 300-500 ml, a drying temperature of the graphite oxide filter cakes after filtering is 30-85° C., and a drying time of the graphite oxide filter cakes is 48-200 hours; and

[0037] (3) grinding the filter cakes after washing by the dilute hydrochloric acid with a grinding equipment, and processing with the heat treatment at a certain high temperature for 15-30 seconds; and obtaining the large graphene sheets; wherein: a yield of graphene of a layer number below 10 is above 90%; the grinding equipment is an edge runner, a vibration mill, a turbine grinder, a jet mill, a fan mill, a sand mill, a colloid mill, a ball mill, or a family-use grinder; and the heat treatment of graphite oxide powders has a temperature ranging from 500-1,350° C. The preferred embodiments are illustrated in detail as follows.

First Preferred Embodiment

[0038] The first preferred embodiment relates to a method for preparing large graphene sheets in large scale, wherein a specific preparation process thereof is showed in FIG. 1, comprising steps of:

[0039] mixing 12 g 500 μm natural flake graphite with 260 ml concentrated sulphuric acid; slowly adding 60 g potassium permanganate in an ice bath; mixing evenly, and reacting in the ice bath for 2 hours; rising a temperature to 35° C.; continuing oxidizing for 48 hours; slowly adding 1.8 L deionized water and then adding 30 ml 20% (V/V) aqueous hydrogen peroxide solution; obtaining a mixed aqueous solution containing graphite oxide; processing the mixed aqueous solution containing the graphite oxide with vacuum filtration, obtaining filter cakes, washing respectively with 1 L 10% (V/V) and 1 L 0.5% (V/V) hydrochloric acid, washing off remaining metal ions and inorganic ions, and then drying at 60° C. for 48 hours; grinding the filter cakes into powders by a family-use grinder, treating for 15 s at 1,050° C., and obtaining the large graphene sheets, wherein a yield of graphene of a layer number below 10 is above 90%.

[0040] For the above obtained large graphene sheets, the graphene of a radial sheet size between 20 μm and 100 μm accounts for 50%, and for 15% over 100 μm.

[0041] FIG. 2 is X-ray diffraction spectra of the graphite, the graphite oxide and the graphene, and as seen from FIG. 2, a characteristic peak of natural graphite powders is at 26.4°, which is a (002) crystal face of a graphite crystal. Calculated from a Bragg diffraction equation, an interlamellar spacing is 0.34 nm. When the natural graphite powders are oxidized, a (002) peak thereof disappears, and a characteristic peak of the graphite oxide is at 10.8° and is a (001) characteristic peak of a crystal face. The corresponding interlamellar spacing is 0.84 nm. And at the position of 26.4°, the graphene shows a characteristic peak (002) that is significantly widened in relation to that of the natural graphite powders, which indicates that the interlamellar spacing of the graphene is larger than that of the natural graphite powders, i.e. the natural graphite powders are exfoliated into the graphene.

[0042] FIG. 3 is a scanning electron microscope (SEM) photo of the prepared graphene, and FIG. 4 is a local transmission electron microscope (TEM) photo of the graphene sheet. As seen from FIGS. 3 and 4, the graphene prepared by the present invention has a large radial sheet size, a flat sheet structure, less crystal defects and a high quality.

Second Preferred Embodiment

[0043] The second preferred embodiment relates to a method for preparing large graphene sheets in large scale, wherein a specific preparation process thereof is showed in FIG. 1, comprising steps of:

[0044] mixing 12 g 500 μm expandable graphite with 720 ml concentrated sulphuric acid; slowly adding 120 g potassium chlorate in an ice bath; evenly mixing and reacting in the ice bath for 48 hours; rising a temperature to 35° C.; continuing oxidizing for 36 hours; slowly adding 2 L deionized water and then adding 240 ml hydrogen peroxide; obtaining a mixed aqueous solution containing graphite oxide; processing the mixed aqueous solution containing the graphite oxide with vacuum filtration, obtaining filter cakes, washing respectively with 2 L 10% (V/V) and 1 L 0.5% (V/V) hydrochloric acid, washing off remaining metal ions and inorganic ions, and then drying at 85° C. for 100 hours; grinding the filter cakes into powders by a family-use grinder, treating for 30 s at 850° C., and obtaining the large graphene sheets, wherein a yield of graphene of a layer number below 10 is above 90%.

[0045] For the above obtained large graphene sheets, the graphene of a radial sheet size between 20 μm and 100 μm accounts for 65%, and for 13% over 100 μm.

[0046] FIG. 5 is Raman spectra of the graphene, the graphite oxide and graphite powders according to the second preferred embodiment, and main characteristic peaks of the graphene of the Raman spectra are D peak (at 1,340 cm.sup.−1), G peak (at 1,580 cm.sup.−1) and 2D peak (at 2,700 cm.sup.−1). A generation process of the D peak involves a defect scattering process of incident photons, therefore, it can reflect a disorder of the graphene caused by groups, defects and edges. The more defects, the higher degree of disorder and the stronger D peak. The graphite powders have increased defects and higher D peak after oxidation and intercalation, and the D peak obviously weakens after high temperature expansion reduction, which indicates that the graphene prepared by the present invention has few defects and a high quality.

Third Preferred Embodiment

[0047] The third preferred embodiment relates to a method for preparing large graphene sheets in large scale, wherein a specific preparation process thereof is showed in FIG. 1, comprising steps of:

[0048] mixing 12 g 300 μm graphite powders with 480 ml perchloric acid; slowly adding 90 g potassium persulfate in an ice bath; evenly mixing and reacting in the ice bath for 20 hours; rising a temperature to 35° C., and continuing oxidizing for 120 hours; slowly adding 2.4 L deionized water and then adding 24 ml hydrogen peroxide; obtaining a mixed aqueous solution containing graphite oxide; processing the mixed aqueous solution containing the graphite oxide with vacuum filtration, obtaining filter cakes, washing respectively with 1.4 L 10% (V/V) and 1 L 1% (V/V) hydrochloric acid, washing off remaining metal ions and inorganic ions, and then drying at 30° C. for 200 hours; grinding the filter cakes into powders by a family-use grinder, treating for 30 s at 500° C., and obtaining the large graphene sheets, wherein a yield of graphene of a layer number below 10 is above 85%.

[0049] For the above obtained large graphene sheets, the graphene of a radial sheet size between 20 μm and 100 μm accounts for 80%, and for 5% over 100 μm.

Fourth Preferred Embodiment

[0050] The fourth preferred embodiment relates to a method for preparing large graphene sheets in large scale, wherein a specific preparation process thereof is showed in FIG. 1, comprising steps of:

[0051] mixing 12 g 400 μm expanded graphite with 240 ml phosphoric acid; slowly adding 60 g potassium dichromate in an ice bath; evenly mixing and reacting in the ice bath for 2 hours; rising a temperature to 35° C., and continuing oxidizing for 48 hours; slowly adding 1.8 L deionized water and then adding 30 ml hydrogen peroxide; and obtaining a mixed aqueous solution containing graphite oxide; processing the mixed aqueous solution containing the graphite oxide with vacuum filtration, obtaining filter cakes, washing respectively with 1 L 10% (V/V) and 1 L 0.8% (V/V) hydrochloric acid, washing off remaining metal ions and inorganic ions, and then drying at 60° C.; grinding the filter cakes into powders by a family-use grinder, treating for 15 s at 1,050° C., and obtaining the large graphene sheets, wherein a yield of graphene of a layer number below 10 is above 90%.

[0052] For the above obtained large graphene sheets, the graphene of a radial sheet size between 20 μm and 100 μm accounts for 70%, and for 8% over 100 μm.

Fifth Preferred Embodiment

[0053] Treating the graphite oxide prepared in the first preferred embodiment for 15 s at 1,350° C., and obtaining large graphene sheets, wherein a yield of graphene of a layer number below 10 is above 90%. Compared with the first preferred embodiment, the graphene obtained after treating at 1,350° C. has a higher quality, and D peak in a Raman spectrum basically disappears, namely a defect and a structural imperfection of the graphene are greatly decreased and reduced at higher temperatures. It shows that: compared with exfoliation and reduction processes at 1,050° C., the exfoliation and reduction processes of the graphite oxide at higher temperatures (e.g. 1,350° C.) lead to less defects and greater degree of reduction, namely, the high-quality graphene is reduced more thoroughly. Intrinsic properties such as electrical and thermal conductivity of the prepared large graphene sheets will be further improved.

[0054] In conclusion, according to the method for preparing the large graphene sheets in large scale provided by the present invention, the graphite intercalation process is in a mild manner, after which post-processes of the graphite oxide such as washing, filtering and drying are very simple and effective, avoiding a series of problems restricting the high-quality and efficient preparation of the graphene arising from washing the graphite oxide to be neutral with a large amount of distilled water. The present invention uses cheap raw materials, has mild conditions, a simple process, a low energy consumption and no need for water washing and an ultrasonic exfoliation, and is environmentally friendly and easy to realize the industrialized mass production. The scale distribution of the graphene prepared by the present invention is between 20 μm and 200 μm, and a regulation of the radial scale and the size distribution of the graphene sheets is achieved through selecting graphite raw materials and controlling reaction conditions. The graphene prepared by the present invention has few defects and a high quality, and is basically able to keep intrinsic properties thereof, especially the electrical and thermal conductivity. The electrical conductivity of the film formed by pump filtration of graphene dispersion liquid is above 600 S/cm, which is able to satisfy the demand for high-quality graphene products of such fields as utilizing mechanical properties of the graphene film, fiber and composites and playing the functional features of the electronic material and functional coating.

[0055] Preferred embodiments of the present invention are described above. It shall be understood that the present invention is not limited to the above preferred embodiments, and those skilled in the art can make different variants and modifications within the scope of the claims, and it shall not affect the substance of the present invention.