A METHOD FOR PRODUCING GRAPHENE FLAKES DIRECTLY FROM MINERAL GRAPHITE

Abstract

The invention relates to a method for producing graphene flakes by electrochemical exfoliation, where electrodes (anode and cathode) together with electrolyte constitute an electrochemical circuit with current flowing through it, characterized in that the electrodes are immersed at least partially in the electrolyte and electrolysis is carried out, during which graphene flakes detach from the electrode to be released into the electrolyte solution and then the exfoliated graphene flakes are recovered from the electrolyte solution.

Claims

1. A method for producing graphene flakes by electrochemical exfoliation, where electrodes (anode and cathode) together with electrolyte constitute an electrochemical circuit with current flowing through it, characterized in that the electrodes are at least partially immersed in the electrolyte and electrolysis is carried out, during which graphite flakes detach from the electrodes to be released into the electrolyte solution, and then the exfoliated graphene flakes are recovered from the electrolyte solution by filtration, then the precipitate is washed with distilled water and dried, wherein the precipitate is taken up in DMF and the obtained suspension is subjected to ultrasound at a frequency of 30 kHz for a period of 15 to 30 minutes, then the precipitate is centrifuged and graphene is recovered from the supernatant thus obtained by evaporating the suspension to dryness by drying (at elevated temperature until a graphene layer is obtained) and/or freeze-drying (graphene powder).

2. The method according to claim 1, characterized in that the anode is mineral graphite, and the cathode is mineral graphite or other conductive material, and the electrolyte is a solution containing sulfur salts (sulfates and/or persulfates) and, optionally, compounds adjusting an electrolyte pH.

3. The method according to claim 1, characterized in that the electrolysis is carried out in two steps, where in the first step the electrodes are activated by applying 2 V DC for a period of 5 minutes, then in the second step a DC voltage is increased to 10-15V and the electrolysis is carried out for a period of 5 to 120 minutes.

4. The method according to claim 1, characterized in that a solution of 0.1 M ammonium sulfate and 0.1 M ammonium persulfate or a mixture thereof in a 99:1 to 1:99 weight ratio is used as the electrolyte.

5. The method according to claim 1, characterized in that the electrolysis is carried out in the presence of an acidic ammonium sulfate solution with pH of 1 to 3 or in the presence of an alkaline ammonium sulfate solution with pH of 8 to 10.

6. The method according to claim 1, characterized in that the anode is a rod or a plate made of material containing over 30% by weight of mineral graphite.

7. The method according to claim 1, characterized in that the cathode is a graphite rod or a metal rod or metal mesh made of metal insoluble in cold sulfuric acid.

8. The method according to claim 1, characterized in that the electrolyte is placed in ice bath and cooled to the 4-8 C.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0021] The object of the invention is illustrated in the drawings, in which:

[0022] FIG. 1 shows a diagram of the method according to the invention;

[0023] FIG. 2 shows an X-ray diffraction pattern of graphene flakes produced by the method according to Example 1;

[0024] FIG. 3 shows a TEM image of graphene flakes produced by the method according to Example 1;

[0025] FIG. 4 shows a Raman spectrum for graphene flakes produced by the method according to Example 1.

DESCRIPTION OF EMBODIMENTS

[0026] The present invention is presented in more detail in embodiments which do not limit its scope.

EXAMPLES

[0027] A graphite rod (graphite content >95%) with dimensions of 1.30.67.2 cm (ANODE) and a graphite rod with dimensions of 0.6310 cm (CATHODE) with attached electrical wires (copper wire) were immersed to of their height in a glass vessel filled with an electrolyte solution, prepared by dissolving 2.4 g ammonium sulfate (NH.sub.4).sub.2SO.sub.4 in 200 cm.sup.3 distilled water, with an electrolyte pH of 6.5. The glass vessel was placed in an ice bath to lower the electrolyte temperature during the process to 4-8 C.

[0028] To activate the electrodes, 2 V DC was applied to the electrodes for 5 minutes, a positive voltage to the anode and a negative voltage to the cathode, respectively.

[0029] After 5 minutes, a DC voltage was increased to 10 V and a proper process of graphite electrolytic exfoliation was carried out for 120 minutes.

[0030] The graphene flakes detaching from the cathode formed a suspension in the electrolyte solution. After the process had ended, the electrodes were removed from the vessel and the graphene flake suspension from the vessel was filtered through analytical filter paper to separate the graphene flakes from the electrolyte solution. The precipitate was washed with portions of distilled water of approx. 250 cm.sup.3 (until a positive reaction of sulfate ions with barium ions endedanalytical control, a positive symptom is the lack of precipitate). The precipitate was then dried at a temperature of 60 C. The dry precipitate was taken up in DMF and the suspension was subjected to ultrasound at a frequency of 30 kHz for a period of 15 to 30 minutes. Subsequently, the precipitate was centrifuged in a centrifuge at 2,500 rpm for 15-30 minutes. The centrifuged precipitate was discarded and the supernatant obtained after centrifugation was used to obtain dry graphene by evaporating the suspension to drynessdrying (at elevated temperature until a graphene layer was obtained) or freeze-drying (graphene powder).

[0031] The graphene flakes thus obtained were subjected to physicochemical tests using structural X-ray (FIG. 2), transmission electron microscopy (FIG. 3) and Raman spectroscopy (FIG. 4). Test results show that the resulting product is characterized by a high content of graphene (over 90%) consisting of single or several flake layers with sizes between 300 nm and 1 m.

Example 2

[0032] The process of graphene electrochemical exfoliation was performed analogously to Example 1, with graphite foil with dimensions of 0.2210 cm (ANODE) and a graphite rod with dimensions of 0.610 cm (CATHODE) immersed in electrolyte with pH=6.5 being used as electrodes. The electrolyte is a mixture of aqueous solutions of 0.1 M ammonium sulfate and 0.1 M ammonium persulfate in a 1:1 volume ratio. Other electrochemical process conditions were used as described in Example 1.

Example 3

[0033] The process of graphene electrochemical exfoliation was performed analogously to Example 1, with graphite foil with dimensions of 0.2210 cm (ANODE) and a graphite rod with dimensions of 0.610 cm (CATHODE) immersed in electrolyte with pH=3 being used as electrodes. The electrolyte is a mixture of aqueous solutions of 0.1 M ammonium sulfate, 0.1 M ammonium persulfate and 2M H.sub.2SO.sub.4 in a 100:100:1 volume ratio. Other process conditions were used as described in Example 1.

Example 4

[0034] The process of graphene electrochemical exfoliation was performed analogously to Example 1, with graphite foil with dimensions of 0.2210 cm (ANODE) and a graphite rod with dimensions of 0.610 cm (CATHODE) immersed in electrolyte with pH=10 being used as electrodes. The electrolyte is a mixture of aqueous solutions of 0.1 M ammonium sulfate, 0.1 M ammonium persulfate and 5M ammonia water in a 100:100:1 volume ratio. Other process conditions were used as described in Example 1.

Example 5

[0035] The process of graphene electrochemical exfoliation was performed analogously to Example 1, with graphite foil with dimensions of 0.2210 cm (ANODE) and a silver plate with dimensions of 0.10.610 cm (CATHODE) immersed in electrolyte with pH=6.5 being used as electrodes. The electrolyte is a mixture of aqueous solutions of 0.1 M ammonium sulfate and 0.1 M ammonium persulfate in a 1:1 volume ratio. Other process conditions were used as described in Example 1.