The XRD spectrum provides a conclusive proof for the degree of
oxidation as the layer distances of starting graphite and the
products are highly different. The typical diffraction peak of native
graphite was observed at about 2u = 268 [d = 0.34 nm, inset in
Fig. 2(d)] and the diffraction peak of GO particles appeared at
2u = 10.78 (d = 0.85 nm, shown in Fig. 2(d)). The disappearance of
peak at 268 and the appearance of peak at 10.78, indicates that the
product is completely oxidized and the exfoliation process
increased the d-spacing by oxidation to 0.85 nm [27].