Longitudinal unzipping of carbon nanotubes to form graphene nanoribbons

Graphene nanoribbons (GNRs), elongated strips of graphite an atom thick, are tipped for a starring role in future electronic devices. Graphene is a conductor, but GNRs express different electronic properties depending on their width. This tunability may make them more attractive than carbon nanotubes in some applications. The production of GNRs in bulk is the next challenge. Here, a team from Rice University reports the production of 100-nm-wide nanoribbons from multi-walled carbon nanotubes by 'unzipping' them with permanganate in acid. The resulting graphene oxide is then reduced to restore electronic conductivity. The process can also make thinner GNRs by unzipping single-walled nanotubes, though more work is needed on ways of disentangling the ribbons produced by this route. Graphene nanoribbons have important electronic properties — as their width increases they change from semiconductor to semi-metal — but it has been difficult to make large quantities. To do so, Tour et al. simply longitudinally unzip multiwalled carbon nanotubes with permanganate in acid to form graphene oxide, which is then reduced to restore electronic conductivity. The ribbons are about 100 nm wide (thinner ones tend to 'mat'), and the authors use them to make field-effect transistors. Graphene, or single-layered graphite, with its high crystallinity and interesting semimetal electronic properties, has emerged as an exciting two-dimensional material showing great promise for the fabrication of nanoscale devices1,2,3. Thin, elongated strips of graphene that possess straight edges, termed graphene ribbons, gradually transform from semiconductors to semimetals as their width increases4,5,6,7, and represent a particularly versatile variety of graphene. Several lithographic7,8, chemical9,10,11 and synthetic12 procedures are known to produce microscopic samples of graphene nanoribbons, and one chemical vapour deposition process13 has successfully produced macroscopic quantities of nanoribbons at 950 °C. Here we describe a simple solution-based oxidative process for producing a nearly 100% yield of nanoribbon structures by lengthwise cutting and unravelling of multiwalled carbon nanotube (MWCNT) side walls. Although oxidative shortening of MWCNTs has previously been achieved14, lengthwise cutting is hitherto unreported. Ribbon structures with high water solubility are obtained. Subsequent chemical reduction of the nanoribbons from MWCNTs results in restoration of electrical conductivity. These early results affording nanoribbons could eventually lead to applications in fields of electronics and composite materials where bulk quantities of nanoribbons are required15,16,17.