Ultrafast and nanomolar level detection of H2S in aqueous medium using a functionalized UiO-66 metal–organic framework based fluorescent chemosensor

Here, we present a 4-nitrophenyl functionalized Zr-UiO-66 MOF (MOF = metal-organic framework) and its applications towards the selective, sensitive and rapid detection of H2S both in the aqueous medium and vapour phase. The MOF material was synthesized using the 2-(nitrophenoxy)terepththalic acid (H2BDC-O-Ph-NO2) linker and ZrCl4 salt in the presence of a benzoic acid modulator. It was carefully characterized by thermogravimetric analysis (TGA), elemental analysis, powder X-ray diffraction (PXRD), FT-IR spectroscopy and surface area analysis. Noticeable thermal stability up to a temperature of 390 °C under air and the considerable chemical stability in different liquid media (H2O, 1 M HCl, glacial acetic acid, NaOH in the pH = 8 to 10 range) confirmed the robustness of the MOF. The BET surface area (1040 m2 g-1) indicated the porous nature of the MOF. Remarkable selectivity of the MOF towards H2S over other potential congeners of H2S was observed in the aqueous medium. A very high fluorescence increment (∼77 fold) was observed after adding an aqueous Na2S solution to the MOF suspension. The MOF probe displayed the lowest limit of detection (12.58 nM) among the existing MOF-based chemosensors of H2S. Furthermore, it exhibited a very quick (60 s) response towards H2S detection. The MOF compound could also detect H2S in the vapour phase as well as in real water samples. Furthermore, we developed inexpensive MOF-coated paper strips for the naked-eye sensing of H2S. A thorough investigation was carried out in order to elucidate the fluorescence turn-on sensing mechanism.