Fluorescence Determination of Nitrite in Water Using Prawn-Shell Derived Nitrogen-Doped Carbon Nanodots as Fluorophores

In this work, we report the synthesis of nitrogen (N)-doped carbon nanodots (N-CNDs) with an N doping level of 3.6 at. % by hydrothermal treatment of prawn shell and their application as fluorophores for selective and sensitive fluorescence detection of NO2- in water. The results demonstrate that NO2- detection by directly fluorescent quenching at N-CNDs fluorophores can achieve an analytical detection linear range up to 1.0 mM with a detection limit of 1.0 mu M. The obtained detection limit of NO2- using N-CNDs fluorophores is dramatically lower than the maximum limit value of 3.0 mg L-1 (namely, 65 mu M) for NO2- in drinking water ruled by the World Health Organization (WHO), which is very important for a practical application of the developed analytical method. The interference experiments indicate that only I- ions among all common anions and cations investigated show very adverse influence on selective detection of NO2- by this developed N-CNDs based fluorescent determination method. Further, the fluorescence quenching of N-CNDs on NO2- concentrations under the given experimental conditions fits a linear Stern-Volmer relationship very well, indicating a dynamic quenching process in this N-CNDs/NO2- fluorescence sensing system. A fluorescent quenching mechanism resulted from the redox reaction between the excited oxidation state of N-CNDs under light excitation and NO2- was proposed based on the experimental results. The findings in this work exhibit the great potential using cheap and abundant biomass-derived N-doped carbon nanodots as fluorophores for selective and sensitive determination of environmentally harmful anions.