A graphene oxide Cookbook: Exploring chemical and colloidal properties as a function of synthesis parameters

Herein, we describe the synthesis of graphene oxide (GO) over a large range of conditions, exploring the effects of reaction temperature, reaction time, oxidant ratio, and sonication time on the chemical and colloidal properties of the product. As a function of reaction parameters, modified from Hummers' method, GO products were characterized and described via a suite of spectroscopic, structural, and morphological techniques, including TEM, UV-vis spectroscopy, XPS, Raman spectroscopy, FTIR, and DLS. Average carbon oxidation state and the yield (upon sonication) were chosen as the two criteria to evaluate synthesized GO materials. It was observed that as reaction temperature increased, GO oxidation state and yield of the sonication step both increased. Further, increasing reaction time and oxidant ratio not only increased the oxidation state, but also had a pronounced effect on the final yield. As synthesized, GO with higher degrees of oxidization exhibited higher negative ζ-potential, slightly smaller hydrodynamic diameter, and higher critical coagulation concentration(s). Data sets collectively demonstrate that carbon oxidation state, functional group ratios, and the aggregation kinetics of GO products can be readily controlled by varying processing time and conditions with expected changes in aqueous behavior(s), including stability/aggregation.