An amine/imine functionalized microporous MOF as a new fluorescent probe exhibiting selective sensing of Fe۳+ and Al۳+ over mixed metal ions

Nowadays metal-organic frameworks with multiple luminescent centers are very fascinating as multifunctional luminescent material because of their luminescence properties, which could be systematically tuned by deliberate use of organic ligands and metal ions. In this research, we explored a microporous mixed-ligand MOF for highly selective and sensitive detection of metal ions. A two-fold interpenetration pillared-layer amine/imine-functionalized MOF known as TMU-۱۶-NH۲, [Zn۲(NH۲-BDC)۲(۴-bpdh)]·۳DMF, have been synthesized via a mixed ligand approach using amino-۱,۴-benzenedicarboxylate (NH۲-BDC) and ۲,۵-bis(۴-pyridyl)-۳,۴-diaza-۲,۴-hexadiene (۴-bpdh) under solvothermal condition. Sensor TMU-۱۶-NH۲ exhibits Al۳+-selective TURN-ON and Fe۳+-selective TURN-OFF type fluorescence emission responses, for which the electrostatic interaction between Fe۳+ and Al۳+ ions and the inner surface of the micropores may play a critical role. Moreover, the sensor TMU-۱۶-NH۲ shows significantly color change from light yellow to orange and colorless with the addition of Fe۳+ and Al۳+ ions, respectively, which is distinguished by naked-eye. More significantly, the remarkable quenching and enhancing effects of TMU-۱۶-NH۲ for Fe۳+ and Al۳+ possess the advantages of good selectivity, fast response time (<۱min), low-cost, as well as very low detection limits of ۰.۷ and ۰.۰۹ µM for Fe۳+ and Al۳+, respectively. Interestingly, the probe exhibits high sensitivity for Fe۳+ and Al۳+ ions, which is far below WHO's acceptable limit in drinking water.