Posidonia oceanica (Mediterranean tapeweed) leaf litter as a source of fluorescent carbon dot preparations

Carbon dots (CDs) represent a new and highly promising class of nanomaterials with a plethora of applications as novel analytical tools. Their physicochemical properties are determined by the nature of the precursors and the conditions used for their preparation. Nowadays, there is an increasing interest on the use of naturally occurring substances and especially renewable material for their synthesis. In this context, we report the hydrothermal synthesis of aqueous fluorescent carbon dot preparations from Posidonia oceanica (Mediterranean tapeweed) leaf litter, thus transforming waste material to valuable analytical tools. The prepared CDs were nearly spherical (size 1-5 nm) and highly soluble in water due to the presence of hydroxyl and carboxyl groups on their surface. They emitted excitation wavelength-dependent fluorescence. The effect of pH and ionic strength were studied as well as the influence of various metal ions. Carbon dots derived from P. oceanica leaf litter in water, in aqueous ethylenediamine solution and in aqueous cysteamine solution gave fluorescence quantum yields of 3.8%, 11% and 10.6%, respectively. Furthermore, we demonstrated that carbon dot preparations derived from P. oceanica leaf litter can be used as analytical reagents for the fluorometric determination of Fe3+, Cr2O72- and CrO42-.