3D Luminescent Amide-Functionalized Cadmium Tetrazolate Framework for Selective Detection of 2,4,6-Trinitrophenol

A new 3D fluorescent amide-functionalized Cd(II)-based metal–organic framework (MOF) with molecular formula [Cd5Cl6(L)(HL)2]·7H2O (1) was synthesized under solvothermal conditions using CdCl2·H2O and 4-(1H-tetrazol-5-yl)-N-[4-(1H-tetrazol-5-yl)phenyl]benzamide (H2L) in DMF/methanol in the presence of conc. HCl. Single-crystal X-diffraction analysis reveals that the 3D framework structure of 1 is constructed from octahedrally coordinated Cd2+ ions interconncted by chloride anions and ditopic tetrazolate-based ligand molecules. The phase-purity of the compound was confirmed by X-ray powder diffraction (XRPD) analysis, infrared spectroscopy, and elemental analysis. Thermogravimetric analysis suggests that 1 is thermally stable up to 300 °C. Steady-state fluorescence titration experiments reveal that activated 1′ can selectively detect 2,4,6-trinitrophenol (TNP) in the presence of other competing nitroaromatic compounds with a detection limit of 42.84 ppb. Recyclability experiments reveal that 1′ retains its initial fluorescence intensity even after several cycles, suggesting high photostability and reusability for long-term sensing applications. The extraordinarily selective fluorescence quenching is assigned to the presence of energy and electron transfer processes as well as the electrostatic interactions of the MOF with TNP. This new 3D amide-functionalized MOF is a potential candidate that can be developed into a highly selective and sensitive sensing device for the in-field detection of TNP.