Increasing reaction time in Hummers’ method towards well exfoliated graphene oxide of low oxidation degree

Graphene oxide (GO) has been synthesized by a modification of the Hummers’ method using different times of reaction of 30, 60, 120, 300 and 540 min while maintaining all other parameters constant and avoiding aggressive posttreatments such as sonication and strong agitation that are known to affect the chemical and structural integrity of the flakes. The morphology of the obtained flakes has been investigated by optical and electron microscopies. Chemical properties of the GOs have been determined by TGA, XRD, Raman, XPS and EDS. The degree of exfoliation strongly increased with the reaction time, while no significant differences were found between the GOs in terms of their chemistry. Thus, we demonstrate that increasing reaction time is enough for the obtention of large-sized and well-exfoliated GO flakes, while maintaining a chemical richness that would be hindered by aggressive exfoliation techniques.