Structural Changes of 2D Fe_xMn_1−xO₂ Nanosheets for Low-Temperature Growth of Carbon Nanotubes

The synthesis of carbon nanotubes (CNTs) is usually done by metallic catalysts with a gaseous carbon precursor at high temperature. Yet, mild synthesis conditions can broaden the application of CNTs and their composites. In the present work, it is unraveled why partially substituted Fe ions in 2D MnO₂ nanosheets lead to the growth of CNTs at low temperatures of 400−500 °C. The local formation of Fe₃C by carbon precursor explains the unusually high catalytic activity of 2D Fe_xMn_1−xO₂ nanosheets for preparing CNTs. Finally, Fe₃C is oxidized to Fe₃C/FeO_x yolk/shell morphology in ambient atmosphere after the CNT formation reaction. These results shed light on the development of novel catalyst materials that allow for efficiently prepare CNTs under mild conditions for their wider use in energy-harvesting applications.