Fig. 5.

The effect of washing on typical graphene oxide derived from low-purity graphite (98% purity). a, b GO washed with 5 M NaOH at 120 °C. a Restacked GO sheets due to the basic washing. b Detail of the boxed region in a showing that the silicon-rich impurities have become more dispersed but have not been removed. c Chemically reduced GO showing the silicon-rich contamination. d NH₄F washed GO. The surface appears cleaner, but this treatment also causes significant agglomeration and restacking of sheets. e–g A comparison of the EDS spectra of the NaOH washed, chemically reduced and NH₄F washed GO in b–d, respectively