Abstract: In this paper, the yellow-green carbon dots (λex=440 nm) with a fluorescence emission wavelength of 535 nm were prepared by a one-step hydrothermal method using dopamine hydrochloride and o-phenylenediamine as raw materials, and then used as fluorescent marker materials for NO2- detection in water samples after purified and separated. The size of the carbon dots is about 3 nm with good dispersion, excellent salt resistance, stable fluorescence under a broad pH value. However, nitrite contaminants in water sources can cause methemoglobinemia disease and has potential carcinogenic risk. The results of the selectivity of the yellow-green carbon dots prepared to detect common contaminants in water samples showed that the carbon dots had a highly specific response to nitrite, and the detection limit was 0.1166 μg·mL-1 (S/N=3, n=3), which meets the requirements of Chinese national standards for determination of NO2-in drinking water (≤1 μg·mL-1). The detection range of 0~60 μg·mL-1 fits the Stern-Volmer equation, and the range of 0~10 μg·mL-1 (y=0.02x+0.000876, R2=0.9868) and 12~60 μg·mL-1 (y=0.011x+0.198, R2=0.9937) have good linear responses. In addition, the recoveries of three spiked water samples are from 90.8% to 100.8% (RSD=0.03 %~0.86 %, n=3) for the validation test. The method of the fluorescent carbon dots marker for contaminants developed in this work is fast and simple, low-cost and has greatly potential in trace nitrite analysis and can be an effective supplementary method for the monitoring of drinking water sources quality.

Key words: One-step hydrothermal method, Carbon dots, NO₂^-, Water quality monitoring