Multifunctional Lanthanide Metal–Organic Frameworks Are Used for Fluorescence Sensing of Bi³⁺, HPO₄^2–, Flu, and PNBA and Application

Using a nitrogen-containing tricarboxylic acid ligand (imidazole-1-yl) benzene-2,4,6-tricarboxylic acid (H₃ttc) and lanthanide metal elements (Dy, Eu, Nd, and Gd), four lanthanide metal organic frameworks (Ln-MOFs) with the same structure, namely, {[Dy₂ (Httc)₃]·1.5DMF}_n(1), {[Eu₂ (Httc)₃]·1.5DMF}_n(2), {[Nd₂ (Httc)₃]·1.5DMF}_n(3), and {[Gd₂ (Httc)₃]·1.5DMF}_n(4), were synthesized under solvothermal conditions. The characterization analysis showed that the four isomorphic Ln-MOFs were trigonal crystals of the <i>R</i>3̅<i>c</i> space group, with good phase purity and thermal stability. Fluorescence analysis showed that complex <b>1</b> can be an excellent fluorescence sensor for Bi³⁺, HPO₄^2–, and fluridine (Flu), while complex <b>2</b> can be an excellent fluorescence sensor for <i>p</i>-nitrobenzoic acid (PNBA). And their sensing mechanisms were discussed in detail. The fluorescent test paper and fluorescent seal were prepared by using the excellent luminescence properties of <b>1</b> and <b>2</b>, and the pesticide on the surface of cherry tomato was detected. The applicability of these MOFs as fluorescence sensors was proved. Therefore, Ln-MOFs are expected to have unpredictable application prospects in the field of environmental detection.