We report the direct formation of multiwalled
carbon nanotubes (MWNT) by ultrasonication of graphite in
dimethylformamide (DMF) upon addition of ferrocene aldehyde
(Fc-CHO). The tubular structures appear exclusively at the
edges of graphene layers and contain Fe clusters. Fc in
conjunction with benzyl aldehyde, or other Fc derivatives, does
not induce formation of NT. Higher amounts of Fc-CHO added
to the dispersion do not increase significantly MWNT formation.
Increasing the temperature reduces the amount of formation of
MWNTs and shows the key role of ultrasound-induced cavitation energy. It is concluded that Fc-CHO first reduces the
concentration of radical reactive species that slice graphene into small moieties, localizes itself at the edges of graphene, templates
the rolling up of a sheet to form a nanoscroll, where it remains trapped, and finally accepts and donates unpaired electron to the
graphene edges and converts the less stable scroll into a MWNT. This new methodology matches the long held notion that
CNTs are rolled up graphene layers. The proposed mechanism is general and will lead to control the production of carbon
nanostructures by simple ultrasonication treatments.
