Defects coordination triggers red-shifted photoluminescence in carbon dots and their application in ratiometric Cr(VI) sensing

Hexavalent chromium ion (Cr(VI)) is one of the most severe environmental nonbiodegradable pollutants. Considering its high biological toxicity, it is of great significance to establish a method for Cr(VI) analysis with high sensitivity and reliability. Therefore, a simple and sensitive ratiometric sensor is developed according to the coordination between Cr(VI) and carbon dots (CDs). In the presence of Cr(VI), the original CDs photoluminescence (PL) emission at 445 nm was significantly shifted to 565 nm and gradually intensified. The coordination mechanism was investigated, the results indicated that the dual-amino groups at ortho-position of benzene ring is critical for this coordination. Under the optimal condition, a good linear relationship between the concentration of Cr(VI) and the PL intensity ratio I565/I445 was obtained from 120 nM to 200 µM, with a low detection limit of 37 nM. Moreover, this method is applied into real water samples analysis with a high quality.