Flexible zwitterionic carboxylate ligand-based metal-organic framework for multifunctional fluorescent test strips toward nitrobenzene (NB), Fe3+, and Cr₂O₇2.

In this study, a novel lanthanide metal-organic framework [Eu(HL)(H2O)3(SO4)2]·0.5Br·0.5H3O (1) was constructed via a solvothermal method employing Eu3+ and 1,1',1″-((2,4,6-trimethylbenzene-1,3,5-triyl) tris(methylene))tris(pyridin-1-ium-4-carboxylate) (H3LBr3). The ligand rarely exhibits a + 1 valence state in 1. The material exhibits excellent fluorescence sensing performance for nitrobenzene, Fe3+, and Cr₂O₇2-, with detection limits of 5.57 × 10-9 M, 2.09 × 10-9 M, and 1.74 × 10-9 M, respectively. Furthermore, a multifunctional fluorescent detection test strip was developed based on 1, enabling rapid, visual detection of the aforementioned pollutants, fully demonstrating the application potential of this lanthanide metal-organic frameworks for the efficient monitoring of environmental pollutants.