Mechanism of carbon nanotubes unzipping into graphene ribbons

The fabrication of graphene nanoribbons from carbon nanotubes (CNTs) treated with potassium permanganate in a concentrated sulfuric acid solution has been reported by Kosynkin et al. [Nature (London) 458, 872 (2009)]. Here we report ab initio density functional theory calculations of such unzipping process. We find that the unzipping starts with the potassium permanganate attacking one of the internal C-C bonds of the CNT, stretching and breaking it. The created defect weakens neighboring bonds along the length of the CNT, making them energetically prone to be attacked too.