A graphene related material with easily tunable morphology

The production of carbon-based films exhibiting high stability, controlled thickness, and tunable performances, still remains an interesting challenge. The set-up of versatile and inexpensive coating methods for the deposition of carbon-based films with controllable morphology and thickness is still a goal in material science research. We developed a new approach for producing graphene-like (GL) thin films through a two steps oxidation/reduction method starting from a nanostructured (high surface) carbon black [1]. The proposed approach for making GL thin films is environmentally advantageous because all procedures are performed in aqueous media, and it is highly compatible to an industrial scale-up process. Thanks to their good stability in water, driven by residuals oxygen functional groups on the GL layers edge, our GL samples appears as a very versatile nanomaterial, suitable for the preparation in aqueous environment of composites with tunable chemical/physical properties such as microporosity, conductivity, catalytic performances and biocompatibility [2-4]. We prepared different GL samples by varying the pH in the water suspension, studying the effect on the morphology of self-assembled GL films. Zeta potentials of the water suspensions were measured to estimate the stability of the suspension at several pH values, and the surface morphology was then studied by Atomic Force Microscopy (AFM). Transmission electron microscopy and AFM showed that the graphenic layers undergo to self-assembling in thin film after drying, thanks to the instauration of hydrophobic interactions between them: the presence of surface carboxylic functional groups, able to drive the surface aggregation in the suspension, has been actually confirmed by x-ray photoemission spectroscopy. The reported AFM results and related discussion show how the surface roughness and morphology are affected by the pH in the preparation process: in particular, the lowest pH sample exhibits a granular surface, while at higher pH more regular morphologies are produced, with interesting observations as concerns the thickness of some surface features. The observations are interpreted in terms of the forces acting in water suspension and of the role of hydrophobic or hydrophilic behaviors. The results demonstrate the possibility to tune the surface properties of GL films by simply acting on the pH of the suspension during the fabrication, and help to understand the microscopic physical mechanisms involved in the film assembly [5].