AbstractsChemistry

Carbon can be found or synthesised in different arrangements, each one with its particular properties. Curiously, the main building block of the majority of these structures (graphene) was first isolated in 2004 by A.K Geim and K. Novoselov. Using graphene layers as a base is possible to derive almost all the other carbon structures. Bucky balls, carbon nanotubes and nanofibers or graphite, all these are examples of different configurations of graphene layers. The properties and applications of each nanomaterial vary depending of this configuration. For example, carbon nanotubes/nanofibers aspect ratio are ideal for create polymer composites using low charges, obtaining new materials with increased mechanical, electrical or thermal properties. On the other side, graphene may be very useful for the fabrication of protective coatings or transparent electrodes. Carbon nanofibers are an interesting nanostructure for using in gas sensing applications. It is known that pure carbon sp2 surfaces are chemically inert because the nature of the bonding. This is the reason that pure carbon nanotubes need a surface treatment for generate defects over its surface in order to create bonding sites for achieving the efficient adsorption of the environmental molecules. On the other hand, the carbon nanofibers have more sp3 bonds exposed due its natural structures allowing an easier natural adsorption of molecules. Moreover, this property allows to the nanofibers being stable in different polar solvents making easier its manipulation. In this work two types of stacked-up carbon nanofibers were used: the bare carbon nanofibers (CNF) and the graphitized carbon nanofibers (CNFG), that are nanofibers treated with a high temperature process in order to eliminate all its impurities and obtain a rearrangement of the crystal structure. The critical role of the surface of the nanofiber in its sensing characteristics justifies the study of the surface chemical properties. In order to do so, the nanofibers were studied using the X-ray Photoelectron Spectroscopy (XPS) technique in order to obtain information of the chemical composition of its surface. It has been found that the graphitication process eliminates all the impurities of the surface, leaving only carbon and oxygen. Oxygen is a surprising finding, as although the amount is low (around 1%), this means that despite the graphitization process there are some functional groups that can survive the treatments although the high temperatures and the reducing atmosphere. Basically, seems that the surviving functional groups are single bonded oxygen and hydroxyl groups, meanwhile the carbonyl groups are the ones that suffers a higher degree of reduction. In order to fabricate the sensor is necessary to find a way to manipulate the carbon nanofibers. The easiest way is using a solvent as a carrier, but the treated CNFG aggregates rapidly in polar solvents. XPS measurements show that the surface becomes more ordered (increase of the sp2 bonds). A close inspection using Transmission Electron…