Solution-processed graphene materials and composites

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Introduction Graphene achieved widespread attention when it was separated from graphite in 2004 using the micromechanical exfoliation (i.e., adhesive tape) method.1 Although micromechanical exfoliation is a straightforward and easily reproduced method that results in high-quality graphene suitable for fundamental studies, it lacks sufficient scalability for the bulk production of graphene-based materials. Similarly, chemical vapor deposition (CVD) of graphene on metal substrates and epitaxial growth of graphene on silicon carbide (see the articles by Nyakiti et al. and Bartelt and McCarty in this issue) are well-suited for planar applications (e.g., integrated circuits), but are not naturally extended to three-dimensional graphene-based composites.2–4 In contrast, solution methods for isolating graphene exhibit several attributes that overcome the limitations of micromechanical exfoliation and high-temperature growth techniques, including (1) utilization of inexpensive graphite powder as the source material, (2) elimination of the need to transfer graphene from the growth substrate, (3) scalability to large-volume processing for industrial applications, and (4) amenability to mixing with polymers or other nanomaterials to form graphene nanocomposites. In this article, we review solution processing of graphene with a particular focus on methods that enable the incorporation of graphene and related materials into bulk materials

and composites. For organizational purposes, the solutionprocessing methods are separated into four major categories: (1) oxidation and subsequent reduction of graphite as a pathway to isolating graphene oxide and reduced graphene oxide, respectively; (2) exfoliation of graphene in aqueous solutions using amphiphilic surfactants; (3) direct exfoliation of graphene in organic solvents; and (4) exfoliation of graphene using intercalation and electrochemical methods. After describing these solution-based methods, we outline the integration of graphene with polymers and other nanomaterials in bulk material and nanocomposite forms. Furthermore, representative applications in energy conversion and storage, catalysis, electronics, and high-strength materials are delineated throughout the article in an effort to foreshadow the expected technological impact of graphene-based materials and composites.

Isolating graphene through solution processing Synthesis and characterization of graphene oxide and reduced graphene oxide Oxidation of graphite to graphite oxide (now commonly called graphene oxide [GO]) traces its origins to 1859, when Brodie used fuming nitric acid and potassium chlorate (KClO3) to oxidize graphite.5 Approximately a century later, Hummers and Offeman developed a procedure for oxidizing graphite that used potassium permanganate (KMnO4) and sulfuric

Laila Jaber-Ansari, Materials Science and Engineering, Northwestern University; [email protected] Mark C. Hersam, Materials Science and Engineering, Northwestern University; [email protected] DOI: 10.1557/mrs.2012.182

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