Visible detection of explosive nitroaromatics facilitated by a large stokes shift of luminescence using europium and terbium doped yttrium based MOFs

Abstract

To use the large stokes shift and low self quenching of luminescence, we have successfully constructed two luminescent yttrium based MOFs doped with europium and terbium, [Y_0.9Eu_0.1(OBA)(Ox)_0.5(H₂O)₂], Y-MOF:Eu and [Y_0.9Tb_0.1(OBA)(Ox)_0.5(H₂O)₂], Y-MOF:Tb through an isomorphous substitution technique using a two dimensional metal–organic framework (MOF) [Y_1.0(OBA)(Ox)_0.5(H₂O)₂], [OBA = 4,4′-oxybis(benzoic acid), Ox = oxalate], Y-MOF, as a structural basis. The structure and size of Y-MOF, Y-MOF:Eu and Y-MOF:Tb were systematically characterized by PXRD, TGA, SEM and EDX analysis. Y-MOF:Eu and Y-MOF:Tb shows high intensity visible red and green emission, respectively, on the exposure of UV light. These emissions of Y-MOF:Eu and Y-MOF:Tb were used for the visible detection of nitro explosives such as 2,4,6-trinitrophenol (TNP), 1,3-dinitro benzene (DNB), 2,4-dinitro toluene (DNT), nitro benzene (NB), 4-nitro toluene (NT) in acetonitrile through luminescence quenching. Y-MOF:Eu and Y-MOF:Tb shows superior sensitivity towards TNP and NT compared to other nitroaromatic explosives. The large stokes shift of Y-MOF:Eu and Y-MOF:Tb allows naked eye detection of these nitroaromatics. The observed K_SV (quenching constant obtained from Stern–Volmer plots) values are in the range 3.2 × 10⁴ to 0.4 × 10⁴ M⁻¹ for Y-MOF:Eu and 3.19 × 10⁴ to 0.47 × 10⁴ M⁻¹ for Y-MOF:Tb. Using these materials ppm level detection of nitro explosives has been achieved.