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

Abstract

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 FexMn1−xO2 nanosheets for preparing CNTs. Finally, Fe3C is oxidized to Fe3C/FeOx 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.

Mechanism of coupled phase/morphology transformation of 2D manganese oxides through Fe galvanic exchange reaction

“…The intensity ratios between L 2 and L 3 white lines ( I ( L 3 )/ I ( L 2 )) as well as the Fe L 2,3 and Mn L 2,3 peak positions are indicators of the average oxidation state of the element, with shifts towards larger energy losses indicating higher oxidation states. 30,31 However, the Fe L 3 peak position is maintained stable at ∼710.2 eV for all materials while the Fe I ( L 3 )/ I ( L 2 ) ratio only suffers from a slight change (Fig. S10,†Table 1).…”