Two Ln-MOFs Based on 4,4',4''-nitrilotrisbenzoic Acid as Multi-Response Luminescence Sensors With High Selectivity and Sensitivity Toward Fe3+ and Cr2O7 2.

Lanthanide metal-organic frameworks (Ln-MOFs) have been widely developed for sensing due to their inherent structural properties and unique lanthanide luminescence characteristics. Herein, a series of Ln-MOFs (Ln = Nd (1), Eu (2), Gd (3), Tb (4), Ho (5)) were successfully synthesized using the ligand 4,4',4''-nitrilotrisbenzoic acid (H₃NTB) under hydrothermal conditions. The fluorescence experiments demonstrate that compounds 2 and 4 can specifically recognize Fe³⁺ and Cr₂O₇ ^2- ions in aqueous solutions through significant fluorescence quenching, respectively. This process not only exhibits high selectivity for the target ions but also shows a low detection limit, excellent anti-interference capability, and relatively fast response time (less than 45 s). The distinct emission changes of 2/4 enable multifunctional, rapid, convenient, and visible detection by the naked eye under 365 nm UV light. Finally, the potential sensing mechanisms were elucidated based on experimental evaluation in detail.