(Invited) Reaction of Elemental Sulfur at the Surfaces of Carbon Nanotubes and Graphene

The chemical functionalization of nanocarbons is key for ensuring their processability in solution and to derive new surface functionalities for applications. For this respect, the oxidation reactions of graphene and carbon nanotubes by strong oxidants is nowadays among the most significant to both clean the raw materials and add functional groups, such as what is present at the surfaces of the graphene oxides (e.g. GO and RGO) and oxidized carbon nanotubes. Because of the harsh conditions ( e.g. strong acids), the oxidation process gives rise to a great variability of surface groups ( e.g. epoxide, hydroxyl, carbonyl) from which the chemical behavior is rather complex. The reaction also leaves acidic residues in quantities that can be environmentally hazardous. Here, we explored an alternative approach to functionalize carbon nanotubes and graphene using a direct reaction with elemental sulfur. Depending on the conditions, we find that the sulfur atoms can modify irreversibly the surfaces with a covalent episulfide functions. The sulfur reaction is extensive, and it is therefore presented here as a green alternative for the chemical processing of nanocarbon materials.