Mechanistic insights into ion-beam induced reduction of graphene oxide: An experimental and theoretical study

Interest in graphene oxide (GO) due to its controllable and adjustable properties has been increasing, especially in the field of electronic and electrochemical charge storage devices. Hence, the modification of surface chemistry and structure of GO can be outlined as crucial for achieving the preferable properties. In this study, we have investigated the influence of 15 keV proton-beam irradiation on GO structure and surface chemistry. The results obtained by Raman spectroscopy, Fourier-transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) were complemented with theoretical ones, obtained by using density functional theory (DFT), semi-empirical (SE) calculations and inelastic thermal spike (iTS) model. The FTIR and XPS results showed that proton irradiation partially reduces the GO with the preferential removal of the alkoxy and epoxy groups. Also, we identified a clear linear relation between the decresase of oxygen content and the decrease of ID/IG ratio i.e. increasing disorder of GO structure. The SE and DFT calculations highlighted a reduction of GO as a single- or multi-step process depending on the type of basal-plane or edge oxygen group. Dynamic SE calculations revealed that for kinetic energy of hydrogen below 1.5 eV the reduction is chemically driven, while at energies higher than 20 eV, the reduction of GO is a result of physical processes. iTS results showed that increase of temperature might contribute to reduction of GO via desorption of epoxy and alcoxy groups, as the least thermally stable groups (T ∼200 °C). The results of this work emphasize the capabilities ion beam irradiation for gradual modification of surface chemistry and structural properties of GO by providing more information about the mechanisms of hydrogen interaction with individual groups, interplay between defect creation, oxygen content and accompaning effects of ion energy loss processes