Ultrafast room-temperature reduction of graphene oxide to graphene with excellent dispersibility by lithium naphthalenide Haesol Jung, Seung Jae Yang * , Taehoon Kim, Jong Hun Kang, Chong Rae Park * Carbon Nanomaterials Design Laboratory, Global Research Laboratory, Research Institute of Advanced Materials, and Department of Material Science and Engineering, Seoul National University, Seoul 151-744, Republic of Korea ARTICLE INFO Article history: Received 11 April 2013 Accepted 19 June 2013 Available online 28 June 2013 ABSTRACT The reduction of graphene oxide (GO) to graphene is typically carried out under very harsh conditions that require strong reducing agents, elevated temperatures, and long reaction times. Here we introduce a new reducing agent, lithium naphthalenide (LN: ), which is distinguished by the very fast (less than 10 min) and highly efficient reduction of graphene oxide, even under ambient conditions. In contrast with conventional reducing agents that yield hydrophobic reduced graphene oxide (r-GO), this new reducing agent produces r-GO with enhanced hydrophilicity and a very stable dispersion in water. As an additional advantage, the dispersibility of the resultant r-GO can be easily controlled by varying the washing conditions. This new reducing agent, LN, opens up a practical and economical route to the production of hydrophilic r-GO and broadens the applications of graphene-based materials. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Graphene is at the center of many current nanomaterials re- search efforts because of its low weight and outstanding mechanical, thermal, physical, and electrical properties [1– 7]. Many techniques, including mechanical exfoliation [8], chemical vapor deposition [9,10], epitaxial growth [11,12], and chemical reduction [13–16], have been employed to pre- pare graphene or reduced graphene oxide. Among these methods, chemical reduction has received significant atten- tion because of its utility in the large-scale production of high-quality graphene, which is an essential prerequisite for practical applications. Chemical reduction methods use reducing agents such as hydrazine [13], sodium borohydride (NaBH 4 ) [14], hydrohalic acid [17], hydroquinone [18], iron nanoparticles [19], and ascorbic acid [20]. Although these chemicals are promising reducing agents, they require elevated (80–120 °C) or low (À33 °C) temperatures and long reaction times (1–24 h, Table 1) [13,14,17,21]. In addition to the drawback of these severe reduction conditions, multi-step processes are sometimes re- quired to achieve effective reduction [14]. To overcome these limitations, considerable effort has been applied to the devel- opment of room-temperature reduction reactions [19,22–24]. However, reduction times at room temperature are generally longer than those of elevated temperature reduction reac- tions, as shown in Table 1. Agents that can reduce graphene oxide (GO) within short periods of time under ambient condi- tions are still required. Reduced GO (r-GO) typically displays low dispersibility in organic solvents, and the low hydrophilicity of r-GO hinders the further r-GO processing required for its applications [25,26]. Efforts have been made to overcome the poor disper- sibility of r-GO, particularly by preparing water-soluble 0008-6223/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.carbon.2013.06.068 * Corresponding authors: Fax: +82 2 885 1748. E-mail addresses: ygundam1@snu.ac.kr (S.J. Yang), crpark@snu.ac.kr (C.R. Park). CARBON 63 (2013) 165 – 174 Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/carbon