Ultrasensitive detection of mercury(II) in aqueous solutions via the spontaneous precipitation of CsPbBr3 crystallites.

Abstract

Mercury(II) is one of the most toxic ions and has the lowest allowed concentration in water. Lowering the detection limits of Hg2+ based on fluorescence methods is challenging compared to the detection of other heavy metal ions. Co-precipitation of the CsPbBr3 precursor and mercury ions in aqueous solutions was developed for the ultra-trace level detection of Hg2+. It was found that the formed CsPbBr3 crystals with sizes in the range of nanometers to micrometers exhibited strong fluorescence in the solid state free of water, and the incorporation of Hg2+ in the crystals would cause fluorescence quenching. Therefore, the decrease in fluorescence intensity could be used to quantitatively detect Hg2+. A microwell array was designed by dispersing the sample solution with the perovskite probe and evaporating water for 3 min to form solid fluorescent crystals, leading to the incorporation of Hg2+ in the crystals. This evaporation-induced co-precipitation strategy successfully solved the problem of the instability of perovskite materials in water. The concentration of Hg2+ can be obtained according to the decrease in the fluorescence intensity, which is caused by the replacement of Pb2+ by Hg2+ in the crystals during the crystallization process. The CsPbBr3 crystallites can be used to detect ultra-trace levels of Hg2+ simply and quickly, with a linear range of 5-100 nM and limit of detection (LOD) as low as 0.1 nM. More importantly, no organic molecules are required to prepare crystals since the micron-sized crystals have obvious fluorescence. This method demonstrates great promise in detecting low concentrations of Hg2+ in aqueous solutions.