Carbon dots codoped with nitrogen and sulfur are viable fluorescent probes for chromium(VI)

Carbon dots codoped with nitrogen and sulfur (N,S-CDs) were synthesized by a single-step hydrothermal method. The N, S-CDs were characterized by transmission electron microscopy, X-ray diffraction, FTIR and X-ray photoelectron spectroscopy in terms of surface morphology, functional groups and surface composition and elemental composition. The CDs possess intense fluorescence and excitation wavelength dependent emission wavelengths. Fluorescence is strongest at an excitation wavelength of 360 nm and typically peaks at 440 nm. The fluorescence of the N,S-CDs is quenched by Cr(VI) ion. Under the 360 nm excitation wavelength condition, fluorescence intensity decreases linearly on increasing the Cr(VI) concentration from 1 μM to 10 μM, and the LOD at a signal-to-noise ratio of 3 was about 0.2 μM. The method was applied to the quantitation of Cr(VI) in spiked real samples and gave satisfactory results.