Fabrication of luminescent Eu(III)-functionalized hydrogen-bonded organic framework for sensitive detection of Th ions.

Thorium (Th) has a wide range of applications in industries such as medicine and the nuclear industry, so it is critical to develop effective detection technologies to avoid the hazards they pose to the environment and human health. In this study, we used 4, 4', 4″-(1, 3, 5-triazine-2,4,6-triyl)tribenzoic acid (HTATB) as the starting material to form a hydrogen-bonded organic framework (TATB-HOF) at room temperature by hydrogen-bonding self-assembly. We then functionalized it with Eu using a post-synthesis modification approach to produce a red-fluorescent HOF(Eu@TATB-HOF). The luminescence mechanism of Eu@TATB-HOF was caused by the ligand-to-metal charge transfer-assisted energy transfer (LMCT-ET) between TATB-HOF and Eu. Eu@TATB-HOF was stable in an aqueous solution and enabled highly sensitive detection of Th. When Th concentrations ranged from 2.0 to 37.0 mmol/L, the fluorescence intensity of Eu@TATB-HOF showed a good linear relationship with the concentration of Th ions, with a detection limit of 1.5 mmol/L. Furthermore, several methods were used to demonstrate that the fluorescence quenching of Eu@TATB-HOF by Th was mostly mediated by the inner filter effect (IFE). Finally, this probe was successfully used to detect Th ions in real samples.