Electrolyte engineering for the mass exfoliation of graphene oxide across wide oxidation degrees†

Oxygen-containing functional groups play crucial roles in graphene oxide due to their enhanced processability, stability, and functionalization. However, achieving precise control over the oxidation degrees of graphene oxide through a straightforward and effective method remains a significant challenge. Herein, we report a two-step electrochemical approach encompassing pre-intercalation and post-exfoliation/oxidation, enabling the mass exfoliation of graphene oxide with customizable oxidation levels. Initially, the pre-intercalation of concentrated sulfuric acid into graphite foil promotes uniform expansion, transforming it into a quasi-monolayer graphene structure. Subsequently, post-exfoliation in reductive/oxidative electrolytes triggers the simultaneous detachment and oxidation process, resulting in well-dispersed graphene nanosheets with quantified oxidation levels on a timescale of minutes. Comprehensive characterization studies confirm the varied oxidation levels of the exfoliated graphene oxide, spanning conventional oxidation degrees obtained via Staudenmaier's, Hofmann's, and Hummers' methods. Furthermore, we evaluate the scalability of this method and the solution processability of exfoliated graphene nanosheets, demonstrating the continuous production of graphene oxide at the kilogram scale and the fabrication of meter-length nanocomposite films with exceptional mechanical properties.