Evaluation of first-row transition metal oxides supported on clay minerals for catalytic growth of carbon nanostructures

In the present work we employed various transition metals (Cr, Mn, Fe, Co, Ni, Cu and Zn) loaded on different smectite clays (laponite and montmorillonite) as catalysts in synthesis of carbon nanostructures (mainly nanotubes) and we report the effect of the nature of the catalytic centers and type of aluminosilicate layers in the morphology, quality and structure on the final products. Owing to their unique swelling, ion-exchange and intercalation properties smectite clays were easily, uniformly and reproducibly loaded with metal cations. Different homoionic forms of montmorillonite and laponite were prepared containing first-row transition metals and the synthesis of carbon nanostructures was carried out at 700 °C using an acetylene/nitrogen mixture. A variety of analytical techniques (XRD, Raman, SEM, TEM and thermal analysis) were used to fully characterize the final materials. Iron-, cobalt-, nickel- and manganese-exchanged clays showed to be effective catalysts for the production of carbon nanotubes, while acetylene decomposition over copper-exchanged clays resulted to the creation of carbon spheres. The resulting hybrid systems are particularly attractive for polymer reinforcing applications since the combined action of clay–carbon nanotubes in polymer matrixes can provide outstanding properties to the resulting composite materials.