Novel Hg (II) selective fluorescent green sensor based on carbon dots synthesized from starch and functionalized with methimazole.

We describe a green new method for the synthesis of water-soluble photoluminescent carbon dots (CDs) that were functionalized with methimazole (MTZ) and applied to determine Hg2+ based on the fluorescence extinction. Starch obtained from rice was used as a natural source for the production of CDs by hydrothermal treatment. Also, it was proposed a factorial design to optimize the parameters for CD synthesis and the results showed that the luminescence intensity is a function of temperature and not of the heating time in the hydrothermal process. The synthesized CDs were characterized using fluorescence techniques, Fourier transform infrared spectroscopy (FTIR), and UV-Vis spectroscopy. Through transmission electron microscopy (TEM) and dynamic light scattering (DLS), it was found the formation of CDs on a nanometer scale with an average size of 11 nm. The functionalization with MTZ, eliminated all interferences from other metals, indicating a selective response to Hg2+ ions. The method was applied to Hg2+ determination in waters. Under optimal conditions, was obtained a limit of detection of 1.8 × 10-7 mol L-1 with a linear range from 3.3 × 10-7 to 50.0 × 10-6 mol L-1. Therefore, the proposed method can be considered a simple, selective, and precise alternative that minimizes the number of reagents used for Hg2+ determination in natural waters, and can be applied on a large scale in environmental analyzes.