Stability of iron-containing nanoparticles for selectively growing single-walled carbon nanotubes

Abstract

The structure and composition of catalyst particles play crucial roles in growing carbon nanotubes (CNTs) during chemical vapor deposition. Particularly, some bimetallic catalysts have been previously reported to synthesize single-walled carbon nanotubes (SWCNTs) with selective chirality. However, the active phase of such bimetallic catalysts has been rarely investigated and the origin of the SWCNT chirality selectivity remains controversial. To fill this gap, we herein study the evolution of an MgO supported FeCu catalyst with the assistance of environmental transmission electron microscopy. It is revealed that the introduction of CO at 600 °C could reduce the catalyst in which the active phase is determined to be Fe2.5C. Large-diameter Fe2.5C particles fluctuate strikingly and catalyze the synthesis of multi-walled CNTs by a tip-growth mode. Whereas small-diameter Fe2.5C particles exhibit high stability and grow SWCNTs with a base-growth mode. Theoretical simulations reveal that the interfacial formation energy between (6, 5) SWCNT and the popular Fe2.5C (311) surface is the lowest, partially accounting for the high selectivity of (6, 5) SWCNTs. This work sheds more lights on the CNT growth mechanisms and could guide the design of novel catalysts for controlled synthesis of CNTs.