Nitrogen-doped carbon quantum dots: Facile synthesis and application as a “turn-off” fluorescent probe for detection of Hg2+ ions

•N-doped carbon quantum dots (N-CQDs) are synthesized by using folic acid as carbon and nitrogen sources.•The N-CQDs with average size of 4.5±1.0 nm exhibit excitation wavelength-dependent fluorescence.•The N-CQDs can serve as an effective fluorescent sensing platform for lable-free sensitive detection of Hg2+ ions.•The N-CQDs-based Hg2+ ions sensor can be applied to real lake water samples with excellent sensitivity and selectivity.

A facile, economical and straightforward hydrothermal strategy is used to prepare highly luminescent nitrogen-doped carbon quantum dots (N-CQDs) by using folic acid as both carbon and nitrogen sources. The as-prepared N-CQDs have an average size of 4.5±1.0 nm and exhibit excitation wavelength-dependent fluorescence with the maximum emission and excitation at 390 and 470 nm, respectively. Furthermore, due to the effective quenching effect of Hg2+ ions, such N-CQDs are found to serve as an effective fluorescent sensing platform for lable-free sensitive detection of Hg2+ ions with a detection limit of 0.23 μM. The selectivity experiments reveal that the fluorescent sensor is specific for Hg2+ even with interference by high concentrations of other metal ions. Most importantly, the N-CQDs-based Hg2+ ions sensor can be successfully applied to the determination of Hg2+ in tap water and real lake water samples. With excellent sensitivity and selectivity, such stable and cheap carbon materials are potentially suitable for monitoring of Hg2+ in environmental application.

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