Eco-friendly sensing of hexavalent chromium ions via copper-doped carbon quantum dots: a fluorescent probe for water safety

Abstract

The hydrothermal synthesis is presented of copper-doped carbon dots (Cu-CDs) from citric acid, urea, and copper chloride, resulting in blue-fluorescent particles with stable emission at 438 nm when excited at 340 nm. Through comprehensive spectroscopic and microscopic characterization (FTIR, XPS, UV, and HRTEM), the Cu-CDs demonstrated remarkable stability across varying pH levels, ionic strengths, temperatures, and UV exposure. Notably, Cu-CDs exhibit ultra-sensitive and selective detection of hexavalent chromium [Cr(VI)] ions in aqueous environments driven by fluorescence quenching. The system showed a robust linear response to Cr(VI) in the 0–80 µM range, with an impressive limit of detection (LOD) of 0.186 µM, significantly lower than the WHO’s permissible limit of 0.96 µM. These findings position Cu-CDs as an effective tool for environmental monitoring and water safety applications.