Nitrogen-doped carbon quantum dots (N-CQDs) with strong blue fluorescence and high quantum yield of 66.8% were synthesized via a facile one-pot hydrothermal treatment with ammonium citrate and ethylenediamine as carbon and nitrogen sources, respectively. The blue fluorescence emission is independent of the excitation wavelengths and is very stable in a wide pH range. These N-CQDs, well dispersed in water and other polar solvents, showed a highly selective and sensitive detection of hazardous and toxic Hg2+ in the range of 10 nM - 20 μM through a fluorescence quenching process. The quenched N-CQDs by Hg2+ exhibited high selectivity and sensitivity for I- in the range of 0.5 μM - 40 μM via a fluorescence recovery process. A possible charge transfer process responsible for the effective detections was proposed according to the UV-Vis absorption and fluorescence decay measurements.

J. Mater. Chem. C, 2014