Graphene-based quantum dots for the detection of heavy metal ions in water

This Ph.D. thesis investigated the possible use of carbon-based nanoparticles to detect the contamination of drinking water by toxic heavy metals. Carbon nanoparticles were synthesized by using different strategies and chemical methods in order to obtain the best material for practical applications. Specifically, starting from C60 fullerene, unfolded fullerene nanoparticles (UFNPs) were obtained through two alternative oxidative procedures. Differently, with a bottom-up approach, graphene oxide quantum dots (GOQDs) were prepared by pyrolysis of citric acid. Both nanomaterials showed fluorescence emission when excited with light in the UV/blue region and the fluorescence intensity was affected by the presence of heavy metal ions in solution owing to diverse mechanisms. By studying the variations of fluorescence together with the changes of the absorption signal, a multiple calibration diagram was obtained in UFNPs, which can be used to univocally identify the types of metal ions and their respective concentrations. A study of the sensing efficiency as a function of the concentration of sensing nanoparticle was also carried out for the first time. UFNPs were also studied for ion removal through metal-induced aggregation processes which lead to precipitation and water purification. Finally, the possibility of achieving solid GOQDs/PVA films was studied in order to make a portable device that allows easier in-field detection of contamination of water samples.