Green Chemistry Dynamic Article Links Cite this: Green Chem., 2011, 13, 2714 www.rsc.org/greenchem COMMUNICATION Facile synthesis of reduced graphene oxide in supercritical alcohols and its lithium storage capacity† Eduardus Budi Nursanto, a,b Agung Nugroho, a,b Seung-Ah Hong, a Su Jin Kim, c Kyung Yoon Chung c and Jaehoon Kim* a,b Received 9th June 2011, Accepted 20th July 2011 DOI: 10.1039/c1gc15678k A facile and green method to produce reduced graphene oxide (RGO) nanosheets based on supercritical alcohols is described. The obtained RGO nanosheets exhibited a high carbon-to-oxygen ratio (up to 11.89, determined by X-ray photoelectron spectroscopy), high electronic conductivity (up to 10 600 S m -1 ), and high lithium storage capacity with good cyclability (652 mA h g -1 at a 50 mA g -1 after 40 cycles) when tested as an anode material. Owing to its superior electrical, optical, chemical, mechanical, thermal and catalytic properties, 1,2 graphene has attracted much attention as a potential material for a wide variety applications including electronic devices, 3 energy storage materials, 4 optical devices, 5 catalysts, 6 and polymer nanocomposites. 7 Develop- ing large-scale, cost-effective graphene production methods is critical for successful use of graphene in industries. Presently, four different methods are reported to produce graphene nanosheets, which include chemical vapour deposition (CVD) of hydrocarbons (e.g., ethylene) on transition metal surfaces, 8 micromechanical exfoliation of graphite to isolate graphene sheets, 9 epitaxial growth of graphene on silicon carbide at high temperatures, 10 and chemical graphitization of exfoliated graphene oxide (GO) to reduced graphene oxide (RGO) in colloidal suspensions under deoxygenated conditions. Among these, the chemical reduction route is considered the most promising and economically viable approach for the large- scale production of graphene. 1 In addition to the scalability a Clean Energy Research Center, Korea Institute of Science and Technology (KIST), Hwarangno 14-gil 5, Seongbuk-gu, Seoul, 131-791, Republic of Korea. E-mail: jaehoonkim@kist.re.kr; Fax: +822958 5205; Tel: +822958 5874 b Clean Energy and Chemical Engineering, University of Science and Technology, 113 Gwahangno, Yuseong-gu, Daejeon, 305-333, Republic of Korea c Energy Storage Research Center, Korea Institute of Science and Technology(KIST), Hwarangno 14-gil 5, Seongbuk-gu, Seoul, 131-791, Republic of Korea †Electronic supplementary information (ESI) available: Experimental and characterization details. XPS survey and high-resolution spectra, UV-vis spectra, Powder conductivity, XPS results of the RGO prepared in supercritical ethanol and prepared using a continuous process. See DOI: 10.1039/c1gc15678k and cost-effectiveness, the chemical reduction route allows versatile adaptation of chemical functionalities, which widens its applications. Typically highly deoxygenated GO sheets that resemble graphene are produced as a colloidal suspension in water or other organic solvents using strong reducing agents such as hydrazine, 11,12 and dimethyl hydrazine. 7 However, the use of highly toxic and potentially explosive reducing reagents is not attractive in commercial-scale applications. In addition, the hydrazine-based method has a risk of heteroatom (e.g. nitrogen) introduction in the reduced GO, which can result in a high resistance. 13 In the past year, various efforts were made to search for ‘green’ alternatives to hydrazine. The alternatives include hydrothermal dehydration, 14 N-methyl-2-pyrrolidinone (NMP)-based solvothermal reduction, 15 and reduction with less or non-toxic reducing agents such as L-ascorbic acid, 16 sugar, 17 and alcohol vapours. 18 The performance of the ‘green’ approaches relative to the hyrazine-based methods were not extensively studied; however, based on the experimentally de- termined features of the RGO, e.g., carbon-to-oxygen ratio and electronic conductivity, the ‘green’ alternatives were not as effective as the previously reported hydrazine-based method. Additionally, relatively lengthy reaction times were necessary for the ‘green’ methods, which is another problem for commercial implementation. Therefore, development of a facile, green, and fast method for the mass production of RGO with a high carbon- to-oxygen ratio and high electronic conductivity remains a great challenge. Recently, we demonstrated that metal nanoparticles (Ni, Ag, and Cu) and low oxidation state metal oxide (Fe 3 O 4 ) nanopar- ticles can be synthesized in supercritical alcohols utilizing the reducing effect inherent to the supercritical alcohols. 19–21 The reducing power of the supercritical alcohol may be attributed to the involvement of dissociated hydroxide ions (OH - ) from alcohol at its supercritical state. 22–24 Supercritical fluids can offer environmentally benign and facile synthetic conditions for the production of nanomaterials owing to their unique physical properties, including low viscosity, fast diffusion, zero surface tension, and tuneable physical properties. 25–27 The rapid reaction rate (less than 1 min) allows us to develop a scalable process for the production of nanoparticles using a flow-type, tubular 2714 | Green Chem., 2011, 13, 2714–2718 This journal is © The Royal Society of Chemistry 2011 Downloaded by Korea Institute of Science and Technology / KIST on 19 September 2012 Published on 11 August 2011 on http://pubs.rsc.org | doi:10.1039/C1GC15678K View Online / Journal Homepage / Table of Contents for this issue