A simple and mild chemical oxidation route to high-purity nano-graphene oxide

Nano-graphene oxide (nGO) is used in a wide range of applications including cellular imaging, drug delivery, desalination and energy storage. Current preparation protocols are similar as for standard graphene oxide (GO) and typically rely on mixtures of sulfuric acid and potassium permanganate. We present a new route to nGO (similar to 30 nm diameter) using a quite defective arc-discharge carbon source and only 9 M nitric acid as the oxidising agent. The preparation can be scaled up proportionately with current GO protocols with 50 mL of half-concentrated nitric acid able to process one gram of arc-discharge material. The workup is straight forward and involves neutralization with sodium hydroxide which precipitates the sodium salt of nGO from solution. The only by-product of the new procedure is aqueous sodium nitrate which makes this protocol the cleanest route yet to nGO. The presence and quantities of functional groups in our nGO are determined and compared with standard GO. We anticipate that this new route to nGO will foster a range of new applications. The presence of highly reactive carboxylic anhydride groups on our nGO material in particular offers an excellent opportunity for purpose-specific chemical functionalization. (C) 2016 Elsevier Ltd. All rights reserved.