sentences:  Large quantities of width-controlled GNRs can be produced via graphite nanotomy, where applying a sharp diamond knife on graphite produces graphite nanoblocks, which can then be exfoliated to produce GNRs.GNRs can also be produced by "unzipping" or axially cutting nanotubes.In one such method multi-walled carbon nanotubes were unzipped in solution by action of potassium permanganate and sulfuric acid.