Graphene oxide nanoplatelets of different crystallinity synthesized from helical-ribbon carbon nanofibers and multiwall
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Cesar Merino Grupo Antolín Ingeniería, E-09007 Burgos, Spain
Mauricio Terronesa) Department of Physics, Department of Materials Science and Engineering & Materials Research Institute, The Pennsylvania State University, University Park, PA 16802-6300; and Research Center for Exotic Nanocarbons (JST), Shinshu University, Wakasato 4-17-1, Nagano 380-8553, Japan
Ignacio Martin-Gullonb) Chemical Engineering Department, University of Alicante, Alicante 03690, Spain (Received 1 June 2011; accepted 5 August 2011)
Graphene oxide nanoplatelets (GONPs) were obtained by unraveling helical-ribbon carbon nanofibers (HR-CNF) using a modified Hummers and Offeman method in conjunction with ultrasonication. In this account, we carry out a complete evaluation of the effect of different oxidative agent concentrations on the resulting platelet materials. Transmission electron microscopy, atomic force microscopy, Fourier transform infrared, x-ray diffraction, x-ray photoelectron spectroscopy, and thermogravimetric analysis were performed to carefully characterize GONPs resulting from the oxidative process. Comparative experiments using multiwall carbon nanotubes (MWCNTs) and graphite were also carried out. Our studies suggest that the oxidation treatment is more effective in HR-CNFs than in MWCNTs. Furthermore, the unraveling of HR-CNFs results in GONPs consisting of less stacked layers when compared to other starting materials such as graphite. Therefore, HR-CNFs appear to be excellent precursors to produce few-layered GONPs. I. INTRODUCTION
This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs. org/jmr-editor-manuscripts/ b) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.272
graphene, but, unfortunately, are not effective for largescale manufacturing.7 Alternative chemical approaches have recently emerged as the best route to obtain graphenes in bulk scale.7–9 Traditionally, these chemical approaches use natural graphite as a starting material.4,10,11 In a first stage, graphene layers within graphite are intercalated and oxidized by reaction with an oxidizing agent in an acid media, thus producing graphite oxide (GO). Subsequently, GO is mechanically or thermally exfoliated4–6,11 to generate graphene oxide or graphene oxide nanoplatelets (GONPs). The high oxidation state observed in GO, results in a low electrical conductivity. To recover in-plane electrical conductivity of GO, it is necessary to reduce the oxide, either chemically using hydrazine4 or thermally in a flowing gas reducing/inert atmosphere.12 Because of the different morphologies of these natural graphites, it has proven difficult to isolate individual GO layers and the yields of monolayer GO with respect to multilayer GO could be extremely low. Very recently, novel methods that result in the formation of graphene and graphene nanoribbons have been reported by unzipping carbon nanotubes (CNTs).13–18
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