Catalytic synthesis of carbon nanofibers with different graphene plane alignments using Ni deposited on iron pillared clays

The present study confirmed that crystalline nanofibers with controlled structure may be prepared at different reaction temperatures over Ni deposited on Fe pillared clays. It was found a large catalytic effect over the growth of carbon nanofibers at temperatures between 450 and 650 °C. TEM pictures revealed different types of CNFs as a function of the reaction temperature: platelet type structures at 450 °C, both platelet and fishbone type structures at 550 °C, and tubular type structures that started to be produced at temperatures above 600 °C. CNFs associated with a reaction temperature of 650 °C were characterized by a very broad diameter distribution; some CNFs had diameters much higher than the freshly reduced metal crystallites. The arrangement of graphite sheets shifted from a situation where a large fraction of the edge sites would be available for gas adsorption to other in which a minor fraction of these sites were available. As a consequence, the CNFs surface area tended to decrease in increasing the reaction temperature. Finally, some improvement of stacking and removal of defects were achieved by raising the reaction temperature.