Upscaling potential of the CVD stacking growth method to produce dimensionally-controlled and catalyst-free multi-walled carbon nanotubes

Multi-walled CNTs (MWCNTs) with structural characteristics optimised for bio-applications have been produced using a catalyst-supported chemical vapour deposition (CVD) method. The upscale potential of the process was demonstrated by combining classical semi-continuous and stacked-growth modes. The vertically aligned MWCNT films thus obtained were multi-layered with five continuous strata of well-structured nanotubes. Following gentle disentanglement, the stacks were converted to individual MWCNTs with short dimensions (a final length and diameter of ～1.2 μm and ～12 nm) and almost catalyst-free (<0.04%). Overall, our process produces dispersed, bio-tailored MWCNTs with an output growth-yield 20 times higher than a standard CVD setup and exempt of complex or destructive post-growth steps of purification and separation. These constitute key steps towards the mass production of MWCNTs with low toxicological risks, an essential prerequisite for biomedical applications.