Copper foils as substrates for growing nitrogen-doped carbon nanotubes

Hybrid Fe- and Cu-based nanoparticles (NPs) embedded in a variety of graphitic carbon matrices were produced using an aerosol-assisted chemical vapor deposition method. A thin copper foil was used as the substrate, and ferrocene and benzylamine were pyrolyzed at temperatures ranging from 750 °C to 950 °C. Three types of hybrid materials were obtained: (1) Fe₃C and Cu NPs encapsulated in graphitic carbon at 750 °C, (2) nitrogen-doped multiwalled carbon nanotubes with a high density of NPs attached to their surface at 800 °C, and (3) a large tubular-defective fiber-type material surrounded by NPs above 850 °C. Backscattering scanning electron microscopy and energy dispersive spectroscopy revealed the composition, morphology, and size of the NPs obtained in each case. Raman spectroscopy characterizations revealed the typical G-band and D-band with<i>I</i>_D/<i>I</i>_Gvalues ranging from 0.79 to 0.88, which are related to the formation of topological defects and highly defective tubule-like graphitic structures. We also correlated the shift of the G-band to lower values with the type of structure obtained by increasing synthesis temperature. The interlayer graphitic distance and Fe₃C- and Cu-NP crystal planes were examined using transmission electron microscopy. Finally, we proposed a formation mechanism for the different hybrid materials involved in the synthesis. Electrochemical impedance spectroscopy results are discussed. Our samples, with their unique properties, can be used as molecular sensors or electrodes in energy storage devices, opening up exciting possibilities for future applications.