Scheme 1

UV-vis absorption spectra of graphene oxide (GRO, blue line), highly reduced graphene oxide (SP-HRG, green line) reduced with PE, chemically reduced graphene oxide (CRG, purple line) and pure root extract (SP, red line). Although the concentration of CRG was the same as that of SP-HRG, it exhibits a much lower absorption coefficient due to its poor dispersibility in water