Surface oxidation of Single Wall Carbon Nanohorns for the production of surfactant free water-based colloids

Single Walled Carbon Nanohorns (CNHs) are tiny graphene sheets, wrapped to form horn-shaped cones with a half-fullerene cap, having 30-50 nm length and 2-5 nm diameter. They generally group together and form aggregates (spherical clusters or bundles) similar to "dahlia" flowers or buds. Stable suspensions of CNHs in water or other polar solvents are useful for several applications, like the case of the use as black liquids in volumetric solar concentrators [1-3] or for subsequent chemical processing of the nanostructures, as in the case of covalent functionalization [4,5]. Since CNHs, as other graphene-based materials, are not easily dispersible in water due to the hydrophobic nature of the surface, usually surfactants are used to achieve proper colloidal stability. Despite the ease of use of surfactants for the stabilization of these colloids, they have some drawbacks like formation of foam, chemical interaction in covalent functionalization, degradation in extreme conditions, easy desorption from the surface to cite some, with consequent destabilization of the colloid. In this work, we exploited the surface oxidation of CNHs to achieve stable suspensions in water without the need of surfactants.