▎ 摘　　要

Functionalization of graphene is fundamental to facilitating its processing and offers a wide scope for advanced applications. Here we demonstrate a facile, highly efficient and mild covalent functionalization of graphene using HNO3 vapour. This results in functionalized few-layer graphene (FLG) that is high in both quantity and quality. We fully characterized the structure and defect level of functionalized FLG by X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy and Raman spectroscopy. The results from this analysis show the tunability of the surface oxygen functionalities of FLG achieved through controlling the oxidation temperature without affecting the major intrinsic properties of graphene. This allows for further doping for applications, for example with nitrogen as a metal-free catalyst in the oxygen reduction reaction.