Controllable functionalization of carbon dots as fluorescent sensors for independent Cr(VI), Fe(III) and Cu(II) ions detection

Abstract Carbon-dots (CDs)-based fluorescent sensors have been successfully used for heavy metal ion detection in drinking water, but the following two points hinder their large scale applications: (1) CDs usually exhibit poor response selectivity for specific ions; (2) there is a lack of multifunctional CDs probes with independent detection of multiple ions. So it’s very urgent to develop multifunctional CDs fluorescent probes for their independent and highly selective detection of multiple ions in water. In this work, carbon nanosheets (CNs) were first stripped from carbon rods by the electrochemical method, and then polymerized into CDs less than 10 nm in size and simultaneously functionalized with ammonia, N,N-Dimethylformamide or polyethylene glycol in the hydrothermal/solvothermal process, respectively. These functionalization can selectively introduce C N bonds, NH2 and OH groups on CDs surface, respectively. These three functionalized CDs exhibit evidently enhanced fluorescence response to Cr6+, Cu2+ and Fe3+ ions, respectively. Compared with the bare CNs, their sensitivity and selectivity can be enhanced by more than 12 and 7 times, respectively. Their limit of detection is reduced by at least one order of magnitude, and the linear response intervals are significantly broadened to low-concentration region (i.e., 0.8–20.0 μM).