Highly Selective and Sensitive Luminescence Turn-On-Based Sensing of Al(3+) Ions in Aqueous Medium Using a MOF with Free Functional Sites.

Abstract

A new metal-organic framework [Co(OBA)(DATZ)0.5(H2O)] {OBA = 4,4'-oxybis(benzoic acid) and DATZ = 3,5-diamino-1,2,4-triazole}, 1, was synthesized by hydrothermal reaction. Single-crystal X-ray data of 1 confirmed two-dimensional rhombus grid network topology with a free nitrogen site of triazole ring and two amine groups of each DATZ. Photoluminescence study of 1 in aqueous medium shows blue emission at 407 nm upon excitation at 283 nm. This emissive property was used for the sensing of Al(3+) ions in aqueous medium through very high luminescence turn-on (6.3-fold) along with the blue shifting (∼24 nm) of the emission peak. However, luminescence studies in the presence of other common metal ions such as Mg(2+), Zn(2+), Ni(2+), Co(2+), Mn(2+), K(+), Na(+), Ca(2+), Cd(2+), Hg(2+), Cu(2+), Fe(2+), Fe(3+), and Cr(3+) in aqueous medium shows luminescence quenching in varying extent. Interestingly, the luminescence turn-on-based selectivity of Al(3+) ions in aqueous medium was achieved even in the presence of the highest quenchable metal ion, Fe(3+). Furthermore, very high sensitivity was observed in the case of Al(3+) ions with a limit of detection of Al(3+) of 57.5 ppb, which is significantly lower than the higher limit of U.S. Environmental Protection Agency recommendation of Al(3+) ion for drinking water (200 ppb).