Controlled synthesis of graphene sheets with tunable sizes by hydrothermal cutting

We report a hydrothermal method that directly reduces graphene oxide (GO) into graphene nanosheets (GNs) with different sizes. In the presence of NaOH and hydrazine, the hydrothermal reaction at 80 °C resulted in the formation of GNs with a lateral size of ~1 μm but the size of GNs decreased to ~300 and ~100 nm upon increasing the reaction temperature to 150 and 200 °C, respectively. The morphology of the resulting GNs was observed by atomic force microscopy and transmission electron microscopy. The thickness of GNs is basically <3 nm, indicates the GNs stack together in a few-layer manner. XRD, XPS, FTIR, and Raman spectroscopy were used to characterize the structural changes before and after reduction. The results suggested that the defect stability in GO and reduced GNs could be responsible for the temperature dependence of the size of reduced GNs. A hydrothermal method is proposed to simultaneously reduce and cut graphene oxide into graphene sheets with different sizes in a controlled manner, in which the reaction temperature as a critical parameter is used to control the size of resulting graphene sheets.