A multifunctional fluorescent zinc(II)-MOF sensor for selective detection of Fe3+/MnO4− and NACs

Multifunctional luminescent sensors play a critical role in protecting human health and the environment by enabling effective monitoring of water contaminants. In this study, a robust three-dimensional zinc(II)-based metal-organic framework ( Zn-MOF ), {[Zn 2 (L-N) 2 ]·5H 2 O·2((CH 3 ) 2 NH 2 )} n , was successfully prepared using 5-(5-carboxypyridin-3-yl) isophthalic acid (H 3 L-N) as the organic ligand. Single-crystal X-ray diffraction analysis revealed that the Zn-MOF crystallizes in the I 2/a space group, featuring a pts topological network with a point symbol of {4 2 ·8 4 }, where Zn 2+ ions (tetracoordinate, tetrahedral geometry) and L-N 3− ligands act as four-connected nodes and linkers, respectively. Fluorescence sensing experiments demonstrated that the Zn-MOF functions as a versatile “turn-off” fluorescent probe with high selectivity and sensitivity toward Fe 3+ , MnO 4 − , and 2,4,6-trinitrophenol (TNP, a nitroaromatic compound, NAC). The Stern-Volmer quenching constants ( K sv ) for Fe 3+ and MnO 4 − were determined to be 3.89 × 10 4 M −1 and 9.25 × 10 5 M −1 , respectively, with a low detection limit for Fe 3+ reaching 10 −5 M. For TNP, the quenching efficiency reached 99.68% with a static quenching constant of 5.08 × 10 3 M −1 . Density functional theory (DFT) calculations and spectral analysis indicated that the fluorescence quenching mechanisms involve photoinduced electron transfer (for TNP) and energy competition (for Fe 3+ and MnO 4 − ). Additionally, the Zn-MOF showed excellent recyclability, maintaining stable sensing performance after at least five cycles. The above results demonstrate that the Zn-MOF is a reliable, multi-responsive sensing platform that could be applied for environmental monitoring.