Herbal mixture-derived carbon dots for selective fluorimetric sensing of Cr6+ in water for environmental applications

Carbon dots derived from natural precursors are presently being used as chemosensors of different metal ions. In the present work, highly fluorescent and photostable carbon dots (CDs) with an average size of 11.4 nm were prepared from a powder mixture of Azadirachta indica , Momordica charantia and Syzygium cumini using hydrothermal process. CDs were further characterized using HRTEM, XRD, XPS, FTIR, UV-Vis and fluorescence techniques. Maximum emission intensity of CDs was recorded at 420 nm on excitation at 330 nm. The quantum yield of CDs was ∼22.8%. CDs selectively detected Cr 6+ ions through visual color change from colorless to yellow. Cr 6+ selectively quenched the emission of CDs due to complexation of the metal ion with the functional groups on the surface and also due to inner filter effect. CDs were able to detect Cr 6+ within a linear range of 2–300 μM and the limit of detection was 0.6 μM. Based on rapid, label free and selective detection of Cr 6+ , the CDs prepared in this work were further used in the analysis of toxic Cr 6+ in real water samples. A very high recovery percentage (93–101%) of Cr 6+ along with good reproducibility in quantitative determination by CDs was observed in different spiked water samples.