Enhanced catalyst nucleation for vertically grafted CNTs in 3D heterostructures on defect-free 2D materials

Abstract

A rationally designed three-dimensional (3D) heterostructure integrating anisotropic low-dimensional materials (such as one-dimensional nanotubes and two-dimensional crystals) exhibits synergistic properties unattainable in individual components. By combining the axial anisotropy of 1D materials with the in-plane characteristics of 2D materials, such architectures offer broad application prospects in areas such as out-of-plane electrical conduction and 3D thermal diffusion. In this study, a 3D chemically bonded heterostructure comprising vertically aligned carbon nanotubes (VA-CNTs) and defect-free graphite was synthesized via optimized Al₂O₃/Fe/graphite catalytic system, forming a 3D VA-CNTs/graphite allotropic heterostructure without an intermediate dielectric layer. Experiments have proved that the presence of amorphous Al₂O₃ effectively confines lateral migration of Fe nanoparticles and suppresses their ripening, thereby reducing the size dispersion of the catalyst particles, ultimately facilitating an ordered growth of VA-CNTs. Furthermore, this confinement mechanism shows its applicability to other 2D materials like h-BN, which broadens its potential applications. This reveals a new way of developing novel anisotropic 3D nanostructures based on hierarchical CNT grafting, allowing the utilization of the intrinsic properties of both nanomaterials, with potential applications in various fields.