A “turn-on” fluorescence sensing for sensitively detecting Cr(Ⅵ) via a guest exchange process in Cu NCs@MIL-101 composites

Copper nanoclusters (Cu NCs) as a new fluorescent material are often used for determining metal ions, but most of them are based on the “turn-off” model. Here, a “turn-on” model of fluorescence sensing platform for the detection of Cr(Ⅵ) have been developed based on Cu NCs@MIL-101 composites. The Cu NCs@MIL-101 were synthesized by a simple mixture of the Cu NCs and MIL-101(Cr), in which the Cu NCs were uniformly distributed in MIL-101(Cr). Notably, the fluorescence intensity of Cu NCs@MIL-101 is significantly weakened due to the internal filtration effect (IFE) of MIL-101. When Cr(Ⅵ) is introduced, the fluorescence of Cu NCs@MIL-101 will be recovered by guest exchange process of Cr(Ⅵ) and the Cu NCs, which will overcome the IFE of Cu NCs@MIL-101. Based on this, a “turn-on” fluorescence probe was successfully constructed for the quantitative detection of Cr(Ⅵ) with two linear ranges of 0.05-1 μM and 1-20 μM, and a low detection limit of 0.05 μM. The proposed fluorescence probe possesses excellent selectivity and anti-interference ability, and has been successfully applied in the detection of Cr(Ⅵ) in real water samples with satisfactory results. This study provides a new approach for the analytical application of Cu NCs.