Carbon dot/carbon nitride composites fluorescent probe for the highly selective detection of Cr(VI) ions

Fluorescence quenching of carbon dots (CDs) has been widely used for ions detection, but it usually exhibits poor selectivity for specific ions, so how to enhance their response selectivity is still an urgent task. In this paper, CDs and carbon nitride (C₃N₄) nanosheets are prepared by pyrolysis and thermal oxidation method, respectively, followed by their ultrasonic mixing to synthesize CDs/C₃N₄ composites. They are characterized by transmission electron microscope, X-ray diffractometer, X-ray photoelectron spectrometer, Fourier transform infrared spectroscopy, UV–vis and fluorescence spectrophotometer. The synthesized CDs and C₃N₄ nanosheets both exhibit strong fluorescence response to multiple ions. As a comparison, CDs/C₃N₄ composites exhibit highly enhanced selectivity to Cr⁶⁺ as a result of partial consumption of -NH₂ groups and C[dbnd]N bonds or their reduced binding ability. Meanwhile, our CDs/C₃N₄ probe exhibits high sensitivity of 54 %, short response time of less than 1 min, low detection limit of 0.39 μM, wide linear response interval of 2.0−80.0 μM and high stability.