Novel 2-hydroxynapthyl functionalized aluminum-based metal-organic framework for fluorescence detection of Zn 2+ in the aqueous medium

Abstract

Abstract A new aluminum-based metal-organic framework (MOF), namelyMIL-53-HNA, was synthesized using low-cost Schiff base linker, 2-(2-hydroxynapthyl-1-imine)terephthalic acid (coded as H2HNA). Because of an excellent fluorescent features of this synthesized MOF, we decided to test its suitability for detecting heavy metal ions in aqueous solution. It is interesting to note that the MIL-53-HNA chemosensor could detect Zn2+ ions in water via turn-on response with good sensitivity and selectivity without being interferedfrom diverse metal ions including Na+, Cd2+, Cu2+, Ni2+, Al3+, Pb2+, Co2+, and Fe3+. The selectivity of this sensortowards Zn2+ ions in aqueous solution could be explained through preferential complexation of these ions via free hydroxyl and imine groups present inside its pore cages. This selective complexation suppressed the photo-induced electron-transfer (PET) process from imine (-CH=N-) double bond to the naphthalene group. This suppression of PET process restored the fluorescence of the naphthalene group in the Zn2+treated MIL-53-HNA chemosensor which ultimatelyled to enhancement of itsfluorescence intensity. Theoreticalcalculations have also been done to provide a thorough explanation of thisturn-on mechanistic response of MIL-53-HNA towards Zn2+ions. Additionally, this sensor showed extremely low limit of detection (LOD), 6.8 µM, demonstrated its exceptional Zn2+ detection capabilities. Low cost, excellent stability, sensitivity, and selectivity are the most promising characteristics of this synthesized chemosensor which make it suitable for wastewater treatment.