Ultraviolet-visible spectroscopy of graphene oxides

Dispersions of few-layer (1-3 layers), multi-layer (4-10 layers) and thick-layer (>10 layers) graphene oxide (GO) were prepared by a modified Hummers method with different mass ratios of KMnO4 to graphite. Ultraviolet-visible (UV-vis) spectroscopic data show that few-layer GO dispersions can be distinguished from multi- and thick-layer dispersions by a more intense peak at 230 nm. Atomic force microscopy (AFM) images of few-layer GO contain a single peak, those of multi-layer GO exhibit a shoulder and those of thick-layer GO do not contain a peak or shoulder. These findings allow qualitative analysis of GO dispersions. X-ray photoelectron spectra (XPS) show that the change of UV-vis absorption intensity of GO is caused by a conjugative effect related to chromophore aggregation that influences the π-π* plasmon peak.