Hydrothermal Synthesis of Nitrogen-Doped Carbon Dots for Selective Fe³⁺ Detection

Carbon dots (CDs) have recently regarded as an attractive fluorescent sensor for water quality detection. However, the actual detection application of CDs is limited owing to the low fluorescence quantum yield (QY) and unclear ion detection mechanism. Here, nitrogen doped CDs (N-CDs) with abundant amide groups, which were easy to prepare using urea and citric acid under mild reaction conditions and displayed great light absorption and strong fluorescence performance with a fluorescence QY of up to 26.6%. More importantly, N-CDs could achieve selective detection of iron ion (Fe³⁺) and its concentrations as low as 0.47 µM in water. Meanwhile, N-CDs exhibited a good linear relationship within the concentration range of 0.5-500 µM of Fe³⁺. This mainly because the introduction of amide groups of N-CDs not only could serve as both donors (NH-), but also acceptors (C = O) for hydrogen bonding, which consequently increased multifunctional fluorescent recognition sites and formed coordination interactions with metal ions, and ultimately achieved fluorescence detection of ions. Therefore, the preparation of N-CDs rich in amide groups provides a promising strategy for rapid and efficient detection of Fe³⁺ ions for water quality detection applications.