Influence of sodium and calcium contaminant in the growth of carbon nanotube on rayon-based carbon fibers

Abstract

This study investigated the role of contaminants commonly found on rayon-based carbon fibers (CF) for the carbon nanotubes (CNT) synthesis. The most common contaminant found on CF is sodium. From the experimental results, sodium contaminant indeed performed as a catalyst, but with low efficiency. However, some CF samples also contained calcium as a contaminant, and Ca presence made higher density and better-quality CNT growth. Probably Ca acts as the reducing agent, keeping Na in metallic form along the entire growth process. XPS data suggests a new view of sodium oxide/hydroxide to sodium carbonate transition after CNT synthesis. On CF samples with calcium, sodium keeps activity and carbonate does not form, differently of the sample containing just Na. CF free of contaminants (PAN-based CF) helps set apart the effects and Raman Spectroscopy picked up sodium and calcium effects on the CNT crystalline quality. The sodium presence in rayon-based CF worsens CNT quality when growing from the foreign iron-cobalt catalyst. By another hand, calcium presence helps keeping iron-cobalt nanoparticles surface reduced. Images of Field Emission Gun Scanning Electron Microscopy (FEG-SEM), Energy Dispersive Spectroscopy (EDS), and X-ray Diffraction (XRD) also supported the analysis.