A carbon dot-based fluorescence method for selective quantification of sulfide in environmental samples

With the rapid growth of agricultural and industrial sectors, a significant quantity of sulfide is released into water resources systems at an increasing rate. This has caused serious environmental problems, which calls for the development of sensitive and selective methods for determining sulfide in environmental samples. In this report, we employed carbon dots (C-dots) as fluorescence emitters and measured the decrease in their fluorescence intensity caused by Ag2S formation. Instead of having free Ag+ cation (which can interact with many other species besides sulfide) in the C-dot solution, we used iodide (I-) to convert Ag+ to one of the least soluble silver salts (i.e., AgI). While AgI interacts with sulfide to form Ag2S (because of the lower solubility of Ag2S), it remains stable against many other anions, thereby offering the method high selectivity. Under optimized experimental conditions, the developed method enabled quantifying sulfide in the range of 1-10 mu M with the low detection limit of 0.48 mu M. The applicability of the method was demonstrated by successful analysis of sulfide in a mineral water, a hot spring water, and an industrial wastewater sample.