Luminescent metal–organic framework-based phosphor for the detection of toxic oxoanions in an aqueous medium

Abstract

A terbium-doped yttrium-based metal–organic framework, [Tb_0.2Y_0.8(FDA)(Ox)_0.5(H₂O)₂]·H₂O, 1 {where H₂FDA = furan-2,5-dicarboxylic acid and Ox = oxalate}, was successfully synthesized using the hydrothermal technique as a phosphor material along with a large Stokes shift and low self-quenching of luminescence for the rapid visible detection of toxic anions in an aqueous medium. To confirm the structure and phase purity of compound 1, single crystals of the isomorphous pure yttrium-based compound [Y(FDA)(Ox)_0.5(H₂O)₂]·H₂O, 1a, were synthesized under similar experimental conditions. The single crystal X-ray data of compound 1a confirmed the three-dimensional metal–organic framework formed by the connectivity of the Y³⁺ ion with furan-2,5-dicarboxylate and the oxalate moiety. The phase purity of compounds 1 and 1a was confirmed by powder X-ray diffraction. Compound 1 was systematically characterized via TGA, SEM and EDX elemental mapping analysis. The aqueous dispersion of compound 1 showed highly intense visible green emission upon excitation at 265 nm. The emissions of compound 1 were utilized for the luminescence-based visible detection of toxic anions in the aqueous medium through luminescence quenching. The observed limit of detection (LOD) was 1.1 nM, 2.2 nM and 6.5 nM for chromate (CrO₄²⁻), permanganate (MnO₄⁻) and phosphates (PO₄³⁻, H₂PO₄⁻ and HPO₄²⁻), respectively, and the observed K_SV values were superior to those of all other metal–organic frameworks previously reported. More importantly, the LODs are significantly lower than the level recommended for these anions towards human life.