Influence of C=O groups on the optical extinction coefficient of graphene exfoliated in liquid phase.

LiLiquid phase exfoliation of graphite is currently one of the most promising graphene production methods at large scale. For this reason, an accurate calculation of the concentration in graphene dispersions is important for standardization and commercialization. Here, graphene dispersions, at high concentrations, were produced by electrochemical exfoliation. Furthermore, a cleaner methodology to obtain graphene oxide by electrochemical exfoliation at high acid concentrations was implemented. The absorption coefficient for graphene and graphene oxide was determined in the optical range ($\alpha_{660nm}=$ 1414 ($\pm$3\%) mL mg$^{-1}$ m$^{-1}$ and $\alpha_{660nm}=$ 648 ($\pm$ 7\%) mL mg$^{-1}$ m$^{-1}$, respectively) with an exponential dependence with the wavelength. The difference in $\alpha$ for both materials is attributed to an increased presence of C=O groups as evidenced by FTIR, UV-vis and Raman spectroscopy, as well as, in the calculation of the opical extinction coefficient and optical band-gap via Tauc-plots.