Nitrogen and Sulfur Codoped Carbon Dots Graphitic Carbon Nitride Composites for Fluorescence Sensing of Mercury Ions

A facile "turn-off" fluorescence sensing approach based on nitrogen and sulfur codoped carbon dots intercalated into graphitic carbon nitride (N, S-CDs@gC₃N₄) has been developed for the selective and sensitive detection of mercury ions (Hg²⁺). The sensor offers the synergistic interaction between N, S-CDs and gC₃N₄, where nitrogen and sulfur doping not only enhances fluorescence properties but also promotes strong Hg-S and Hg-N binding affinity. Upon interaction with Hg²⁺ the fluorescence of the N, S-CDs@gC₃N₄ composite is significantly quenched via static quenching mechanism (excitation/emission at 370/425 nm). The sensor shows a linear response to Hg²⁺ in the range of 1.0-7.2 μM (R² = 0.99) with a limit of detection of 0.421 μM. The method was successfully applied to detect Hg²⁺ in spiked tap and canal water samples at concentrations of 1.01, 2.84, and 4.47 µM, yielding recoveries of 98.89%-99.21% (RSD: 0.74%-2.26%) for tap water and 96.76%-98.03% (RSD: 0.61%-1.59%) for canal water. These results demonstrate the potential of N, S-CDs@gC₃N₄ for real-time application of Hg²⁺.