On the evolution of oxidative etching of few layer graphene (FLG) in FLG /TiO2 nanocomposites. Interfacial dipole signature and chemical shift in C1s X-ray photoemission spectra

We present the effect of oxidative etching in FLG/TiO$_2$ hybrids on FLG edges chemistry/morphology addressing also the catalytic activity of TiO$_2$ NPs. According to the XPS and TGA analysis the oxidation degree strongly depends on TiO$_2$:FLG ratio. The preparation of two series of FLG/TiO$_2$ hybrids via sol-gel method and in-situ oxidation permitted to correctly describe and distinguish the chemical composition, core shift and charge distribution in C1s XPS with Tip peak as reference. Such analysis is challenging in carbon materials due the overlapping of C1s peaks from the sample and adventitious carbon reference. We claim the formation of interfacial dipole as possible direct signature of charge transfer from TiO$_2$ to FLG. A downward shift of C1s (sp$^2$C) up to 1.4 eV is measured and contributions of non sp$^2$C are determined in the composites. The modifications related to the oxidation are supported by TEM/SEM observations, and referred to non-catalytic oxidation and oxidation in mechanically mixed components. KEYWORDS: oxidative etching, graphene edges, TiO$_2$ catalyst, interfacial dipole, XPS, charge transfer