▎ 摘　　要

This work explored the synthesis of rGO sheets from graphene oxide (GO) using hydrazine solvent as reducing agent through chemical reduction. Meanwhile, GO films with a 2D structure were prepared from graphite flakes (starting material with an average flake size of 150 urn) by an Improved Hummer's method. Results showed that the chemical oxidation of graphite flakes carried out at room temperature could be used to prepare GO sheets in the initial stage. The conversion of GO into large-area rGO sheets with similar to 85% of carbon content could then be achieved by chemical reduction. RGO sheets with a lateral dimension of up to similar to 45 nm were obtained, which indicated the formation of an extremely thin layer of rGO sheets. A high degree of GO reduction was also realized using a high stirring speed (1200 rpm) for 72 h in a mixture of acids and potassium permanganate, resulting in a high carbon content of rGO with a large lateral dimension and area. Overall, our Improved Hummer's method with a high stirring speed (1200 rpm) for 72 h provided an easy approach to the preparation of large-area and ultrathin rGO sheets. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.