Hydrothermal synthesis of carbon quantum dots as fluorescent probes for the sensitive and rapid detection of picric acid

Heteroatom doping is an efficient approach to regulate the fluorescence properties of carbon nanodots. Herein, novel water-soluble and highly fluorescent nitrogen-doped carbon dots are synthesized via an effective hydrothermal method using mandelic acid and ethylenediamine as carbon and nitrogen sources, respectively, without further chemical modification. The quantum yield of the obtained nitrogen-doped carbon dots is as high as 41.4%. Then, the surface morphology and optical properties of the synthesized nitrogen-doped carbon dots are characterized. The results reveal that the nitrogendoped carbon dots are spherical in shape with an average diameter of 2.5 nm and they emit bright blue fluorescence with an emission peak at about 429 nm (excited at 342 nm). Additionally, the high quantum yield nitrogen-doped carbon dots are employed to detect picric acid selectively and sensitively via the fluorescence quenching phenomenon based on a possible fluorescence resonance energy transfer process. A good linear relationship in the range of 0.5-30 mmol L-1 is obtained with a detection limit of 0.041 mmol L-1 (S/ N = 3). Eventually, the nitrogen-doped carbon dots are applied for the detection of picric acid in actual water samples with recoveries in the range of 94.92-107.84% and relative standard deviations of 1.64-2.80%.