Highly Selective and Sensitive Luminescence Turn-On-Based Sensing of Al3+ Ions in Aqueous Medium Using a MOF with Free Functional Sites

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).