Revisiting graphene oxide chemistry via spatially-resolved electron energy loss spectroscopy

摘要

The type and distribution of oxygen functional groups in graphene oxide and \udreduced graphene oxide remain still a subject of great debate. Local analytic techniques\udare required to access the chemistry of these materials at a nanometric scale. Electron\udenergy loss spectroscopy in a scanning transmission electron microscope can provide the\udsuitable resolution, but GO and RGO are extremely sensitive to electron irradiation.\udIn this work we employ a dedicated experimental set-up to reduce electron illumina-\udtion below damage limit. GO oxygen maps obtained at a few nanometres scale show\udseparated domains with diferent oxidation levels. The C/O ratio varies from about 4:1 to 1:1, the latter corresponding to a complete functionalization of the graphene flakes.\udIn RGO the residual oxygen concentrates mostly in regions few tens nanometres wide. Specific energy-loss near-edge structures are observed for diferent oxidation levels. By combining these findings with first principles simulations we propose a model for the highly oxidized domains where graphene is fully functionalized by hydroxyl groups forming a 2D-sp3 carbon network analogous to that of graphane.