Foxtail millet-derived highly fluorescent multi-heteroatom doped carbon quantum dots towards fluorescent inks and smart nanosensors for selective ion detection

Carbon quantum dots (CQDs) are attracting enormous attention as a smart material owing to their congenital virtues. Unfortunately, their low quantum yield (QY) and modest fluorescence stability seriously restrain their practically versatile applications. Herein, a facile yet green strategy has been developed for synthesizing nitrogen/sulfur/phosphrous (N/S/P) co-doped CQDs via hydrothermal treatment of natural foxtail millet without any extra additives or organic agents. The resultant N/S/P co-doped CQDs were endowed with remarkable excitation-dependent emission, high QY (similar to 21.2%), superior fluorescence stability, and long lifetime (similar to 2.05 ns) owing to multi-heteroatom doping. Thanks to their strong blue-green fluorescence upon irradiation with UV light (365 nm), the water-soluble CQDs demonstrated huge potential for anticounterfeit application as a fluorescent ink. When utilized as a fluorescent sensor for cation determination, the multi-heteroatom doped CQDs especially displayed the highest sensitivity and selectivity for Fe3+ along with good linear correlation ranging from 5 to 150 mu M and a low detection limit of 0.046 mu M. More remarkably, our fabricated high-quality CQDs would hold great promise in analytical and/or environmental fields.