Studies of Fe-binding sites within multiwall carbon nanotubes using Mossbauer spectroscopy

The potential applications of carbon nanotubes (CNTs) are strongly related to their physical and chemical properties. In this work, results of different methods for the oxidation of crude CNTs are reported. These methods changed Fe binding sites within multiwall carbon nanotubes (MWCNTs). Mossbauer spectroscopy was used to detect the chemical properties of the Fe-phases in MWCNTs. Signals from the iron carbide Fe3C were the main components in the Mossbauer spectra of unmodified MWCNTs revealing magnetic ordering even at 300 K. In oxidized MWCNTs, the amount of Fe3C decreased and gamma-Fe and alpha-Fe, ferrihydrates of iron oxides and different forms of goethite appeared. In MWCNTs oxidized with HClO4, a significant fraction (similar to 24%) of magnetically ordered Fe2O3 particles was detected. This study showed that traces of iron catalyst embedded in MWCNTs could be used as a sensitive probe to monitor various MWCNT modifications. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim