Similarities and differences in O 2 chemisorption on graphene nanoribbon vs. carbon nanotube Alejandro B. Silva-Tapia a , Ximena Garcı ´a-Carmona a , Ljubisa R. Radovic a,b, * a Department of Chemical Engineering, University of Concepcio ´ n, Concepcio ´n, Chile b Department of Energy and Mineral Engineering, Penn State University, University Park, PA 16802, USA ARTICLE INFO Article history: Received 20 July 2011 Accepted 18 October 2011 Available online 22 October 2011 ABSTRACT A computational chemistry study was conducted to reveal similarities and differences in the adsorption of molecular oxygen on the edge sites of a carbon nanotube (CNT) and a graphene nanoribbon. Two prototypical CNT molecules with a carbene and a carbyne active site were selected, and this in turn defined two corresponding graphene molecules obtained by CNT unzipping. Their electronic and thermochemical properties before and after O 2 adsorption were compared using density functional theory at the B3LYP/3-21G * level, as implemented in the Gaussian03 software. The sensitivity of the results to the basis set used and the selected CNT diameter was also assessed. Despite significant curvature in a subnanometer-diameter CNT, more similarities than differences were revealed with respect to graphene, both in their charge density distributions and thermochemical prop- erties. Contrary to intuitive expectations, the intrinsic activity of an edge site (at least in the prototypical O 2 chemisorption process) is therefore not significantly modified when graph- ene is rolled up into a nanotube possessing a relatively large degree of pyramidalization. Greater differences exist between armchair and zigzag edges in both CNT and graphene. Both undergo a two-step mechanism of O 2 adsorption, but O 2 dissociates only on the arm- chair edge. Non-dissociative adsorption on an isolated zigzag site has both a lower affinity and a higher activation energy than the dissociative adsorption on the armchair site. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction The discovery of fullerenes [1] and nanotubes [2] has been the trigger for the nanotechnology revolution. Together with the more recent discovery that graphene can be a material in its own right [3,4], this has opened new molecular engineering opportunities for carbonaceous solids and has ushered in the age of ‘nanocarbons’. At the fundamental level, it has raised important new questions regarding the surface chem- istry and chemical reactivity of sp 2 -hybridized carbon atoms. Of special interest here is the role of curvature in altering the electron density distribution in graphene and thus in affect- ing the (re)activity of edge sites, which are known to be much more susceptible to chemisorption of reactive fluids than the carbon atoms in the graphene basal plane or on nanotube walls [5]. The electronic properties of both carbon nanotubes (CNTs) and of a single graphite sheet (graphene) have been the object of close scrutiny over the past two decades and beyond, and a voluminous literature is available [6–8]. Much less is known about the key details of graphene edge chemistry in either flat or curved sp 2 -hybridized carbon materials. The objective of the present study is, therefore, to extend our analysis of edge sites [9] to a comparison of a graphene nanoribbon with that of an analogous CNT. In the interim, the evidence for the existence of carbene-type zigzag sites has become stronger [10–16]; 0008-6223/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2011.10.028 * Corresponding author at: Department of Energy and Mineral Engineering, Penn State University, University Park, PA 16802, USA. E-mail address: lrr3@psu.edu (L.R. Radovic). CARBON 50 (2012) 1152 – 1162 Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/carbon