A pyrene hydrazone-CTAB platform: Achieving sequential distinct sensing for thorium(IV) and uranium(VI) in water

Thorium and uranium found in polluted water and soil caused by mining are ‌posing ecological security risks and being detrimental to sustainable development of the nuclear energy. Reported chemical sensors exhibit excellent response to uranium or thorium, but most of them only capable of detecting one type of the two nuclide ions in organic solvents or in aqueous organic solvent mixture. So it is still a challenging journey to detect the two nuclides distinctly by a same probe in pure water, especially in the presence of coexisting lanthanide interfering ions. In this work, sequential fluorescence detection of Th 4+ and UO 2 2+ in nearly 100% water (H 2 O/DMSO = 100/1, v /v) is achieved by a fluorescent probe, N′-(pyren-1-ylmethylene)-4-hydroxybenzohydrazide ( POH ), with the assistance of cationic surfactant cetyltrimethylammonium bromide (CTAB). POH exhibited a distinct green fluorescence toward Th 4+ in CTAB aqueous solution, and the detection limit can reach 60.2 nM with a binding constant of 7.07 × 10 4  M −1 . Moreover, the CTAB- POH -Th 4+ system presented a selective “turn-off” phenomenon for UO 2 2+ with a high immunity to other interference ions. The detection limit of 88.1 nM toward UO 2 2+ can be reached, with an association constant of 8.17 × 10 4  M −1 . 1 H NMR and FT-IR spectroscopic analysis coupled with nuclide ion titration investigations demonstrated that the presence of CTAB facilitated the formation of POH-Th 4+ excimer, while the addition of UO 2 2+ replaced the Th 4+ , leading to specific emission quenching of the excimer, which was supported by DFT calculations. This study provides a reliable sensing strategy for the sequential detection of Th 4+ and UO 2 2+ in water. It also offers valuable insights into surfactant-assisted sensing mechanism. The probe-CTAB platform also demonstrates the practical applicability to detect the two nuclides in real water samples.