Graphitic carbon nitride quantum dots as an off-on fluorescent switch for determination of mercury(II) and sulfide

A rapid method has been developed for the determination of Hg(II) and sulfide by using graphitic carbon nitride quantum dots (g-CNQDs) as a fluorescent probe. The interaction between Hg(II) and g-CNQDs leads to the quenching of the blueg-CNQD fluorescence (withexcitation/emission peaks at 390/450nm). However, the fluorescence can be recovered after addition of sulfide such that the turn-off state is switched back to the turn-on state. The g-CNQDs were fully characterized by transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, UV-vis absorption and fluorescence spectroscopy. Under the optimal experimental conditions, this probe is highly selective and sensitive to Hg(II). The linear response to Hg(II) extends from 0.20 to 21M with a detection limit of 3.3nM. In addition, sulfide can be detected via the recovery of fluorescence. The linear response range for sulfide species is from 8.0 to 45M with a detection limit of 22 nM. The mechanism of the turn-off-on scheme is discussed. The methods have been applied to the analysis of spiked tap water, lake water and wastewater samples.