Controlling the quantity of γ-Fe inside multiwall carbon nano-onions: the key role of sulfur

One of the most interesting structural features of multiwall carbon onions (MWCNOs) and nanotubes (MWCNTs) is the excellent chemical stability, which allows in situ encapsulation of chosen magnetic materials of interest and multifunctional applications. In this letter, we present an innovative chemical vapour synthesis (CVS) approach, in which the inclusion of small quantities of sulfur during the pyrolysis of ferrocene/dichlorobenzene mixtures allows for an important control in the relative abundance of FCC gamma-Fe, up to a maximum value of similar to 86.5% (structural- and phase-control). The variation in the relative percentage of the encapsulated Fe-based phases was estimated by employing X-ray diffraction (XRD) and Rietveld refinement analyses. The magnetic characterization was achieved by employing superconducting quantum interference device (SQUID) magnetometry, with zero field cooled (ZFC) and field cooled (FC) curves acquired at applied fields of 300 Oe and similar to 50 000 Oe.

Automated summary

One of the most interesting structural features of multiwall carbon onions (MWCNOs) and nanotubes (MWCNTs) is their excellent chemical stability, which allows for in situ encapsulation of chosen magnetic materials and multifunctional applications. This letter presents an innovative chemical vapour synthesis (CVS) approach that incorporates small amounts of sulfur during pyrolysis to control the abundance of FCC gamma-Fe in the material's structure, up to a maximum value of approximately 86.5%. The variation in the relative percentage of the encapsulated Fe-based phases was estimated using X-ray diffraction (XRD) and Rietveld refinement analyses. Magnetic characterization was performed using superconducting quantum interference device (SQUID) magnetometry with zero field cooled (ZFC) and field cooled (FC) curves.