Tuning the oxygen functional groups in graphene oxide nanosheets by optimizing the oxidation time

The most widely used method for the synthesis of graphene in large scale is through the thermal exfoliation and reduction process of graphene oxide (GO). Well know that the physicochemical properties of graphene greatly affected by the oxidation time employed in GO preparation. In this study, GO samples were prepared at different oxidation time through the Hummers' method. The formation of oxygen containing functional groups in GO and their influences onto its’ structure were analyzed and compared. XPS analysis and 13C NMR revealed the formation of carboxyl groups mainly formed at a longer oxidation time. XRD results obtained indicated that the oxidation time have no effect on the interlayer spacing (d) once it reached the optimal extent, however, the graphite stacking order was disrupted due to the insertion of oxygen-containing functional groups. The influence of oxidation time on the stability of GO dispersions was evaluated by zeta potential, which exhibited higher zeta potential and stability at longer oxidation time. This study demonstrates that the integrity and physicochemical properties of GO can be tuned and depend on the type of oxygen-containing functional groups generated at the basal or edge structure, which may foster a range of new applications.