In a deviation from the conventional Hummers method, a spontaneous expansion approach was introduced with expanded graphite as the precursors. The intercalating agent (H2SO4) was able to penetrate into the expanded graphite; this had further expanded the graphite and as a result, a foam-like intermediate was produced. The foam-like graphite was more easily oxidized in reaction with the oxidant (KMnO4) to form graphene oxide (GO). Fully exfoliated GO was obtained with expanded graphite having the median diameter ~ 15 {\mu}m as the precursors. This procedure was much safer and productive in scalable applications than the conventional Hummers methods.
@article{arxiv.1301.3253,
title = {Massive production of graphene oxide from expanded graphite},
author = {Ling Sun and Bunshi Fugetsu},
journal= {arXiv preprint arXiv:1301.3253},
year = {2013}
}