All carbon non-covalent exohedral hybrids: C₆₀ aggregates on nanotube networks

Exohedral van der Waals (vdW) hybrids comprising pristine carbon nanotubes (CNTs) and C₆₀ fullerenes are expected to enable the engineering of carbonaceous materials with tunable physical and chemical properties due to the unperturbed sp² hybridization of the comprising allotropes. In spite of theoretical predictions, experimental realization of exohedral non-covalent hybridization of unmodified C₆₀ fullerenes and CNTs was not reported before, probably due to the relatively strong inter-fullerene and inter-tube interactions that drive the system toward phase separation and the formation of fullerene crystals and CNTs bundles. Here we describe a two-step process for preparation of C₆₀–CNTs hybrids. The first step is based on solution-assembly of random, 3D-networks of individual, pristine CNTs followed by fast solvent-quenching. In the second step sublimated fullerenes are deposited onto the pre-assembled networks where structural defects serve as nucleation points for fullerite nanocrystals. Annealing at low temperature (80 °C) results in re-organization of the C₆₀ nanocrystals into nanometric layers, forming a CNT-C₆₀ core-shell like cylindrical hybrids. Raman characterization and the observed high mobility of the fullerenes at the CNT surface support the assumption that the exohedral hybrids are of vdW type. The approach presented here offers a pathway for preparation of exohedral hybrids with controlled nano-morphology: CNTs-networks decorated by nanometric C₆₀ crystals and CNTs-3D-networks coated by a shell of non-covalently bonded mono- or multi-layers of C₆₀ molecules that may serve to shape the nano-morphology of the active layer in polymer-fullerene bulk-heterojunction solar cells.