Can reduced graphene oxide look like few-layer pristine graphene?

Abstract

The discovery of graphene brought several similar structures, highlighting its main derivative, reduced graphene oxide (rGO). Such structures can be obtained through several simple synthesis methods, mainly from variations of the Hummers method followed by chemical reduction using the most different reducing agents. This has helped to increase its applicability, but there always has been a gap related to the structural quality of the final material, which can still be filled. Therefore, to overcome the density of defects in the Hummers method, instead of creating another variation, we seek to improve existing methodologies, by controlling the KMnO4 addition rate and the temperature of the system. This control leads to a shorter oxidation stage compared to the literature, favoring the graphite oxidation reaction in a controlled and selective way, and producing a graphene oxide (GO) with excellent structural quality. After, through the reduction using hydrazine vapor, a remarkably high quality (HQ) material, the rGO HQ, could be produced. Raman results showed that the rGO HQ has a very low defect density with an average defect distance around 20 nm, which to the best of our knowledge is among the best values ascribed for this kind of graphene derivatives. Four probe measurements revealed low sheet resistance values with high transmittance, additionally, synchrotron infrared nanospectroscopy and density functional theory revealed the preferential formation of epoxy groups on GO HQ flakes as the main reason for its high structural quality. These impressive results allow us to state that our improved methodology produced a rGO HQ with characteristics very similar to those of few-layer pristine graphene without long-term procedures, new steps, or equipment, with the possibility of obtaining large scale production.