Novel fluorescent recoverable probe based on carbon quantum dots/polypyrrole composite for the simultaneous determination of chromium(VI) and sulfite

A novel carbon quantum dots/polypyrrole (CDs/PPy) composite fluorescence probe with excellent selectivity and high fluorescent stability was successfully designed and fabricated by microwave method. PPy was selected as the surface passivating agent to improve the quantum yield (QY) of CDs, which has been demonstrated having a QY enhancement effect, for CDs, from the original value of 12.79% up to 43.68% (CDs/PPy). The fluorescence of CDs/PPy can be effectively quenched by chromium(VI) (Cr(VI)) via inner filter effect (IFE). Importantly, upon addition of sulfite (SO 3 2− ), the fluorescence intensity of the CDs/PPy-Cr(VI) system was recovered through the reduction of Cr(VI) to Cr(III) and inhibited the IFE process between CDs/PPy and Cr(VI). Accordingly, the efficient composite fluorescent probe was established to determine Cr(VI) in aqueous solution and the representative reductive substance SO 3 2− in food. The excellent determination performance and satisfied linear response ranges of the proposed fluorescence probe were obtained over the range of 0.01-250.00 µmol/L and 5.00-250.00 µmol/L with the low detection limits of 2.40 nmol/L and 121.00 nmol/L for Cr(VI) and the representative reducing substance SO 3 2− , respectively. Meanwhile, the fluorescence probe has been successfully applied in determination of Cr(VI) and SO 3 2− in real samples with satisfactory results.