Graphene oxide sheet, article containing graphene-containing substance produced by reducing the graphene oxide sheet, and process for production of the graphene oxide sheet

1. A method for producing a graphene oxide sheet which changes to a compound having a graphene structure when reduced, the method comprising:

(a) dispersing a graphene-containing carbon substance, having aggregates, with a dispersant to reduce the size of the aggregate units and to form a colloidal solution containing the graphene-containing carbon substance;

(b) adding an oxidizing agent to the colloidal solution from step (a), and removing water by lyophilization to adjust the water content to 10 wt % or less to obtain a water-removed composition, the water-removed composition being a powder composition containing the oxidizing agent and the graphene-containing carbon substance; and

(c) mixing the water-removed composition from step (b) with concentrated sulfuric acid to oxidize the graphene-containing carbon substance.

2. The method according to claim 1 , further comprising centrifuging the colloidal solution to remove the aggregates.

3. The method according to claim 1 , wherein the dispersant is a surfactant.

4. The method according to any one of claims 1 to 3 , further comprising after step (c), purifying the resultant graphene oxide sheet by an ion exchange treatment.

5. The method according to claim 1 , wherein the oxidizing agent is permanganate or peroxodisulfate.

6. The method according to any one of claims 1 to 3 , wherein the graphene-containing carbon substance is one or more substances selected from the group consisting of a carbon nanotube, a carbon nanofiber, a carbon fiber, a carbon nanohorn, graphite and a fullerence.

7. The method according to claim 3 , wherein the surfactant is contained in an amount of 0.01 wt % to 10.0 wt %, based on the weight of the graphene-containing carbon material.