Selective Process To Extract High-Quality Reduced Graphene Oxide Leaflets

One popular approach to prepare graphene on a large scale consists of converting graphene oxide (GO) into reduced graphene oxide (RGO). However, this procedure yields graphene flakes with various amounts of oxygenated defects. Using a double liquid phase extraction technique (DLPE) assisted by cholesterol-based polymers, we demonstrate that the RGO flakes of the highest quality, i.e., those with the highest π-conjugated network and with the lowest number of oxygenated defects, can be selectively extracted in isooctane, while lower quality flakes remain in water. Thus, it is possible to collect single-layer graphene sheets of high quality, as characterized by Raman spectroscopy (ID/IG below 0.2) starting from a RGO containing a heterogeneous mixture of leaflets (ID/IG ～ 1.3). The high quality of the RGO leaflets extracted by DLPE was also confirmed by X-ray photoelectron spectroscopy, photoluminescence, Fourier transform infrared spectroscopy, X-ray diffraction, and atomic force microscopy. The conductivity of the films prepared with DLPE RGO flakes is an order of magnitude higher than the one of the films prepared with as-prepared RGO. The thermal stability of the extracted leaflets, as measured by thermal gravimetric analysis, is also greatly enhanced. Thus, sorting RGO by DLPE is a valuable process for the large-scale production of high-quality graphene