Waste-derived carbon nanodots for fluorimetric and simultaneous electrochemical detection of heavy metals in water

A simple and efficient synthesis of carbon nanodots (CNDs) was proposed by using hydrochar obtained through hydrothermal carbonization of beer bagasse (BB), a by-product of the beer industry that possesses several appealing advantages as a lignocellulosic source for carbon material synthesis. Raw materials and produced CNDs were characterized by several techniques such as transmission electron microscopy (TEM), X-ray diffraction (XRD), FT-IR, CHNS elemental analysis, diffusion light scattering (DLS), and zeta potential, and the optical properties were studied by spectrofluorophotometry (PL) and UV-vis absorption spectroscopy. The synthesized CNDs exhibited small dimensions, interesting fluorescence behaviour, high stability and remarkable water solubility due to the presence of hydroxyl and carboxyl functional groups. Exploiting these properties, CNDs were employed in the development of highly sensitive fluorimetric and electrochemical probes for heavy metal ions, which are of great concern for human health, aquatic life, and environmental sustainability. Hg2+ and Pb2+ were detected by the fluorimetric probe with a limit of detection of 11.3 nM and 78.8 nM, respectively, while the electrochemical platform allowed the selective and simultaneous detection of heavy metal ions, reaching a detection limit of 124 ng L−1 and 551 ng L−1, respectively for mercury and lead ions with high sensitivity, in the range between 11.4 and 34.1 μA nM−1 cm−2.