Green Synthesis of Self Assembled Nanospherical Dysprosium MOFs: Selective and Efficient Detection of Picric Acid in Aqueous and Gas Phase

This work demonstrates the solvothermal synthesis of two new lanthanide-based MOFs, namely [{Dy(2N 3 -TPA) 2 (H 2 O)(CH 3 OH)}] ∞ ( 1 ) and [{Dy 4 (5N 3 -IPA) 6 (DMF) 3 (H 2 O) 4 }(DMF)(H 2 O) 2 ] ∞ ( 2 ), derived from two carboxylate ligands, namely 2-azidoterephthalate (2N 3 -TPA) and 5-azidoterephthalate (5N 3 -IPA), respectively, with immobilized azide functionalities oriented toward the pore surfaces. Singlee-crystal X-ray diffraction (SXRD) analyses reveal that 1 exhibits an infinite 1D network while 2 displays a 2D sheet structure with helical metal carboxylate chains. Both compounds are found to exhibit excellent thermal and aqueous phase stabilities. A simple and convenient route has been adopted to reduce the particle size of the as-synthesized compounds to prepare nanoscale metal–organic frameworks (NMOFs). Unprecedentedly, nanospherical architectures are observed for both cases on SEM and TEM analyses. These NMOFs have been successfully exploited as fluorescent probes for the detection of various nitro analytes such as nitrotoluene (NT), nitrobenzene (NB), 2,6-dinitrotoluene (DNT), 4-nitrobenzoic acid (4-NBA), picric acid (PA), etc. As suggested by the values of quenching constants obtained from Stern–Volmer plots, the sensitivity of both NMOFs toward PA sensing is exceptionally high. Furthermore, time-resolved fluorescence studies and theoretical calculations have been performed to speculate the excited state interaction of NMOFs with PA specifically. Moreover, the selectivity toward PA sensing in the presence of other structurally similar nitro analytes and excellent reusability of the employed sensory platforms manifest great potentials of these materials for real-life applications.