Mercaptopropionic acid-capped Mn-doped ZnS quantum dots and Pb2+ as sensing system for rapid and sensitive room-temperature phosphorescence detection of sulfide in water

As a kind of serious concern environmental toxic pollutants, sulfide is widely used in various industrial processes, and generated from the process of biological metabolism. However, the sensitive, rapid and effective detection of sulfide still remains challenge. In this paper, a simple and rapid room-temperature phosphorescence (RTP) method for the detection of sulfide with a high selectivity and sensitivity was proposed by using mercaptopropionic acid(MPA)-capped Mn-doped ZnS quantum dots (QDs) and Pb2+ as a sensing system. Highly water-soluble MPA-capped Mn-doped ZnS QDs with phosphorescence emission property were successfully synthesized by microwave-assisted hydrothermal synthesis method. We discovered that the as-prepared QDs displayed effectively phosphorescence quenching to Pb2+ in pH 11.5 borax-NaOH buffer solution, then demonstrated remarkable phosphorescence recovery after the addition of sulfide to the QDs-Pb2+ system. Therefore, based on the phosphorescence "off-on" behavior of MPA-capped Mn-doped ZnS QDs, a simple, sensitive and selective phosphorescence method for rapid detection of sulfide was successfully developed. The quenching and recovery of the phosphorescence of MPA-capped Mn-doped ZnS QDs have been studied in detail. Under the optimized conditions, the recovered degree of RTP intensity had a very good linear relationship with sulfide concentration in the range of 2 x 10(-7)-80 x 10(-7) mol L-1 with a correlation coefficient of 0.9982, and a lower detection limit of 6.89 x 10(-8) mol L-1. The relative standard deviations for eleven times repeated detections of 5 x 10(-6) and 8 x 10(-6) mol L-1 sulfide were 3.24% and 4.50%, respectively. The proposed method could effectively avoid the interferences of common anions, fluorescence substances and scattering light. Furthermore, it was successfully applied to detect sulfide in real water samples with satisfactory results, and the recoveries were in the range from 94.2% to 107.1%. This work will provide the basis of method for the development of fast and on-line monitoring sensors of small molecule pollutions in water.