Quenching of Photoluminescence of Carbon Dots by Metal Cations in Water: Estimation of Contributions of Different Mechanisms

All carbon nanoparticles with a developed surface exhibit photoluminescence (PL), the surface origin of which makes it possible to create environmental nanosensors based on it. The active development of sensors for metal ions based on the photoluminescence of carbon dots (CDs) has shown that the quenching of CDs' photoluminescence can occur due to different mechanisms. However, the magnitude of their contributions to total PL quenching has not been studied. This article presents the results of studies of the mechanisms of photoluminescence quenching in aqueous solutions of carbon dots of hydrothermal synthesis by metal cations: Co2+, Cu2+, Mg2+, Ni2+, Pb2+, Zn2+, Al3+, Cr3+, and Fe3+. It was established that, for different ions, the following mechanisms make significant contributions to the quenching of the photoluminescence of carbon dots in water: the effect of an inner filter; static quenching due to changes in luminophores caused by (de)protonation of the surface groups of carbon dots with a change of pH value; dynamic quenching. Their contributions to the total quenching of photoluminescence of nanoparticles and the limits of detection were quantitatively determined. The conducted research can be used as an algorithm for the analysis of photoluminescence quenching of carbon nanoparticles by any ions in complex media.