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graphene sheets from graphene oxide by hot-pressing

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CARBON 54 (2013) 143–148 Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/carbon High quality graphene sheets from graphene oxide by hot-pressing Yupeng Zhang a, Delong Li a, Xiaojian Tan a, Bin Zhang a, Xuefeng Ruan a, Huijun Liu a, Chunxu Pan a,*, Lei Liao a,*, Tianyou Zhai b, Yoshio Bando b, Shanshan Chen c, Weiwei Cai d, Rodney S. Ruoff c a School of Physics and Technology, Center for Electron Microscopy and MOE Key Laboratory of Artificial Micro- and Nano-structures, Wuhan University, Wuhan 430072, People’s Republic of China b International Center for Young Scientists (ICYS) and International, Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan c Department of Mechanical Engineering and The Texas Materials Institute, University of Texas at Austin, One University Station C2200, Austin, TX 78712, USA d Department of Physics Xiamen University, Xiamen 361005, People’s Republic of China ARTICLEINFO Article history: Received 24 August 2012 Accepted 7 November 2012 Available online 14 November 2012 1. Introduction Since its successful isolation by mechanical exfoliation [1,2], graphene has attracted a strong recent interest. It is a promis- ing material for energy-storage, interfacing to biological mate- rials, for electronic and optical devices, and other applications [3,4], due to its unique physical, chemical and mechanical properties, which include high values of Young’s modulus (1100 GPa) [5,6], specific surface area (calculated value, 2630 m2 g1) [7], thermal conductivity (5000 Wm1 K1) [8], mobility of charge carriers (exceeding 200,000 cm2/V s) at room temperature [9], saturation velocity (4.5 · 107 cm/s) [10], and critical current densities (3 · 109 A/cm2) [11]. Methods of obtaining C-pure graphene sheets is thus of strategic interest. A variety of methods exist for synthesizing graphene sheets with either top-down or bottom-up approaches. ABSTRACT We report a simple and effective route to convert graphene oxide sheets to good quality graphene sheets using hot pressing. The reduced graphene oxide sheets obtained from graphene oxide by low temperature thermal exfoliation are annealed at 1500 °C and 40 MPa uniaxial pressures for 5 min in vacuum. No appreciable oxygen content was observed from X-ray photoelectron spectroscopy and no D peak was detected in the Raman spectrum. The graphene sheets produced had a much higher electron mobility (1000 cm2 V1 S1) than other chemically modified graphenes. Ó 2012 Elsevier Ltd. All rights reserved. Graphene or chemically modified graphene can be made from four different methods including mechanical exfoliation, chemical exfoliation, epitaxial growth on SiC and chemical vapor deposition on metal surfaces [12–16]. Mechanical exfo- liation, epitaxial growth on SiC, and chemical vapor deposi- tion yield ‘C-pure’ graphene sheets, which are very useful as attractive electronic materials for further micro- and nano- electronics. However, the relatively small yield and high costs have limited its development in electrodes of lithium ion bat- teries and supercapacitors, hydrogen storage, composites reinforcement, catalysis, and so on. ‘Chemical exfoliation’ is employed for ‘large scale’ (gram-scale and larger) production of ‘graphene’ sheets. However, the defects and some chemical functional groups such as hydroxyl (CAOH), carboxyl (C@O, O@CAOH), and epoxide group (CAOAC) could be introduced on the graphene sheets inevitably, which alters the physical * Corresponding authors: Fax: +86 27 68752003. E-mail addresses: cxpan@whu.edu.cn (C. Pan), liaolei@whu.edu.cn (L. Liao). 0008-6223/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.carbon.2012.11.012

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