A turn-on fluorescent sulfide probe prepared from carbon dots and MnO2 nanosheets.

A turn-on fluorescent sulfide probe was prepared from carbon dots (CDs; synthesized using an environmentally friendly method) and MnO2 nanosheets. In this composite probe, the fluorescence of the CDs (with excitation/emission peaks at 330/430 nm) is quenched by the MnO2 nanosheets through an inner filter effect. Introducing sulfide causes the MnO2 nanosheets to be disintegrated through a redox reaction between sulfide and MnO2. Hence, the blue fluorescence of the CDs is restored. Under the optimum conditions, fluorescence increases linearly in the 2-25 µM sulfide concentration range. The detection limit is 0.8 µM. The method was used to analyze spiked real water samples, and satisfactory results were achieved. Graphical abstract Schematic of the detecting sulfide ions using the carbon dots/MnO2 fluorescence probe based on the recovery of carbon dot fluorescence when sulfide ions are added.