Journal of Alloys and Compounds 536S (2012) S450–S455 Contents lists available at SciVerse ScienceDirect Journal of Alloys and Compounds j our na l ho me p ag e: www.elsevier.com/locate/jallcom Preparation, characterization and fundamental studies on graphenes by liquid-phase processing of graphite J.I. Paredes ∗ , S. Villar-Rodil, P. Solís-Fernández, M.J. Fernández-Merino, L. Guardia, A. Martínez-Alonso, J.M.D. Tascón Instituto Nacional del Carbón, INCAR-CSIC, Apartado 73, 33080 Oviedo, Spain a r t i c l e i n f o Article history: Received 17 June 2011 Accepted 3 October 2011 Available online 18 October 2011 Keywords: Graphene Graphene oxide Colloidal suspension Reduction a b s t r a c t Liquid-phase processing of graphite and graphite derivatives is one of the most promising methodolo- gies for the mass production of graphene. Here, we present a brief overview of the main developments in this research area over the last few years, together with our own contributions to the field. Particularly, we discuss the preparation of graphenes both in aqueous and organic media by reduction of exfoliated graphite oxide as well as by direct exfoliation of pristine graphite, highlighting some of the obstacles that have been encountered along the way and the approaches proposed to overcome them. Some fundamen- tal aspects of graphenes derived from graphite oxide, specifically their structure and reactivity, are also considered. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Graphene, a single layer of sp 2 -hybridized carbon atoms, has become the subject of enormous interest and dedicated efforts from the research community in recent years. The unexpected isolation of this material in 2004 by a simple approach of micromechani- cal cleavage of bulk graphite provided access to experiments that were previously regarded unattainable on account of the assumed thermodynamic instability of two-dimensional crystals [1,2]. The subsequent discovery of unusual phenomena and unsurpassed electronic, mechanical, thermal and optical properties has made graphene reach the status of exceptional material with a huge potential in a number of technological uses, which include elec- tronic devices, sensors, composite materials, energy generation and storage or biomedicine [2,3]. The successful implementation of graphene in large-scale applications will critically depend, among other factors, on the availability of simple and cost-effective methods that allow its mass production. At present, the two general approaches that show the highest expectations in this regard are (1) chemical processing of graphite and graphite derivatives (most notably graphite oxide) to obtain colloidally suspended graphene in aqueous and organic media [4], and (2) chemical vapour deposition (CVD) of hydro- carbons (e.g. methane) onto suitable transition metal substrates, particularly copper [5]. The specific characteristics of the produced ∗ Corresponding author. Tel.: +34 985 11 90 90; fax: +34 985 29 76 62. E-mail address: paredes@incar.csic.es (J.I. Paredes). materials differ substantially depending on the chosen approach, and even on the particular method for a given approach. Therefore, in the current state of developments the choice of method for pro- ducing graphene should be mainly determined by its final intended use [6]. In particular, graphenes prepared as colloidal suspensions in the liquid phase are especially prone to further chemical pro- cessing (e.g. functionalization with molecules, nanoparticles, etc.), which is advantageous for the synthesis of hybrid structures and composite materials with a view to, e.g. energy or biomedical appli- cations [4,7]. Progress in the generation and use of colloidally suspended graphene has been rapid and significant over the last few years. Here, we provide a brief overview of the progress achieved in this area together with our own contributions to the field, which have mainly focused on (1) the preparation of graphene either by chem- ical reduction of graphene oxide in aqueous and organic medium or direct exfoliation of pristine graphite in water in the presence of surfactants, and (2) the investigation of some fundamental aspects of reduced graphene oxide. 2. Liquid-phase production of graphenes 2.1. Graphene derived from graphite oxide (reduced graphene oxide) Graphite oxide is a strongly oxygenated derivative of graphite that is produced by the use of aggressive acids and oxidants. Its preparation was documented as early as 1859 by Brodie [8], and over the next century other chemists proposed some variants to 0925-8388/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2011.10.025