A Ni-MOF as Fluorescent/Electrochemical Dual Probe for Ultrasensitive Detection of Picric Acid from Aqueous Media

A water-stable, microporous, luminescent Ni(II)-based metal–organic framework (MOF) ( Ni-OBA-Bpy-18 ) with a 4- c uninodal sql topology was solvothermally synthesized using mixed N-, O-donor-directed π-conjugated co-ligands. The extraordinary performance of this MOF toward rapid monitoring of mutagenic explosive trinitrophenol (TNP) in aqueous and vapor phases by the fluorescence “Turn-off” technique with an ultralow detection limit of 66.43 ppb ( K sv: 3.45 × 10 5 M –1 ) was governed by a synchronous occurrence of photoinduced electron transfer–resonance energy transfer–intermolecular charge transfer (PET-RET-ICT) and non-covalent π···π weak interactions, as revealed from density functional theory studies. The recyclable nature of the MOF, detection from complex environmental matrices, and fabrication of a handy MOF@cotton-swab detection kit certainly escalated the on-field viability of the probe. Interestingly, the presence of electron-withdrawing TNP decisively facilitated the redox events of the reversible Ni III/II and Ni IV/III couples under an applied voltage based on which electrochemical recognition of TNP was realized by the Ni-OBA-Bpy-18 MOF/glassy carbon electrode, with an excellent detection limit of ∼0.6 ppm. Such detection of a specific analyte by MOF-based probe via two divergent yet coherent techniques is unprecedented and yet to be explored in relevant literature.