ABSTRACT

Graphene aerogels are very useful materials for those technological applications where high surface development and good electrical conduction characteristics are required, for example, supercapacitors. Such nanostructured materials can be prepared by drying a highly concentrated graphene colloid; however, poor mechanical stability is typically achieved. In order to provide better mechanical resistance to this material, graphene aerogels can be cross-linked by pure elemental sulfur (heating the sulfur/graphene aerogel blend at 180°C). In particular, graphene is a very good substrate for chemical functionalization by radical addition reactions, since its reactivity is comparable with that of other polycyclic aromatic hydrocarbons. The presence of carbon-carbon double bonds (C═C) makes this material an adequate substrate for radical addition reactions. For example, sulfur molecules (S8) decompose at liquid state, producing linear biradicals c-S8→ ⋅ l-S8 ⋅ (λ-transition), which are able to graft the graphene-based framework of the aerogel, thus cross-linking it. Such a chemical process signicantly improves the material mechanical stability. Scanning electron microscopy images of the graphene-sulfur system (after this cross-linking process) showed the presence of sulfur molecules at the edges of neighboring GNP unities. X-ray energy dispersive spectroscopic mapping was carried out to verify the composition of such materials. Furthermore, differential scanning calorimetry was used to study the kinetic behavior of such cross-linking treatment; in fact, the complete sulfur-carbon network formation was evidenced by the progressive disappearance of the λ-transition signal of the pure sulfur phase. The amount of residual sulfur  in the chemically modied material was evaluated by thermogravimetric analysis and it corresponded to ca. 30% by weight.