Fluorescent graphene oxide derived from carbonized citric acid for copper(II) ions detection

Fluorescent graphene oxide (GO) nanoparticles were obtained from the thermal carbonization of citrate acid. Depending on the synthesizing temperature, the size of GO varied from several to several hundred nanometers. Owing to the confinement from the size, green and blue emissions at around 504 and 450 nm were observed from the GO suspension. These emissions could be dynamically quenched by titrating against copper (II) (Cu²⁺) ions, and the emission intensity was reduced exponentially as a function of Cu²⁺ concentration. The quenching mechanism was ascribed to the bridging of the surface –COOH and –OH groups by Cu²⁺, which restricted the vibration of edge atoms or clusters and reduced the number of luminophores of GO nanosheets. As a result, the concentration of Cu²⁺ was detectable with the fluorescent intensity of GO.