Functionalized graphene quantum dots as a fluorescent “off–on” nanosensor for detection of mercury and ethyl xanthate

A simple, economical and efficient method is introduced for the functionalization of graphene quantum dots (GQDs). The GQDs was synthesized by the thermal pyrolysis of citric acid then mono-ethanolamine (MEA) was used to functionalize its surfaces. The resultant MEA-functionalized GQDs (MEA-GQDs) had remarkable fluorescence emissions with high quantum yield. The interaction studies showed that the fluorescence emissions of MEA-GQDs quenched selectively in the presence of Hg 2+ ions due to the complex formation of Hg 2+ ion with functional groups on MEA-GQDs. Further studies showed that, in the presence of ethyl xanthate ions (EtX − ), the intensity was recovered because of the formation of a stronger complex between the thiol group of EtX − and Hg 2+ ions and the dissociation of the previous weaker complex between MEA-GQDs and Hg 2+ ions. In the optimal conditions, Hg 2+ and EtX − ions could both be detected in the concentration ranges of 0.05–5 and 0.05–3 µM with limits of detection of 10 and 30 nM, respectively. The new MEA-GQDs-based nanosensor was successfully applied for the determination of Hg 2+ and EtX − ions in spiked groundwater as a real sample with the satisfactory recovery of 97.6–101%.