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(2N3-TPA)2(H2O)­(CH3OH)}]∞ (1) and [{Dy4(5N3-IPA)6(DMF)3(H2O)4}­(DMF)­(H2O)2]∞ (2), derived from two carboxylate ligands, namely 2-azidoterephthalate
(2N3-TPA) and 5-azidoterephthalate (5N3-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.