A luminescent anionic Cadmium(II)-MOF for the detection of nitrophenol compounds and metal ions in an aqueous solution

An anionic MOF, namely, {(CH3)2NH2)2[Cd(µ4-PPTA)]·DMF·7H2O}n (1) was synthesized with 4,4′,4″,4‴-(1,4-phenylenbis(pyridine-4,2,6-triyl))tetrabenzoic acid (H4PPTA) and characterized. X-ray results showed that 1 had a four-fold interpenetrating 3D framework with dia topology and the charged balance was provided by dimethylamine cations in the framework. Due to the high emission property and stability of 1 in water, the luminescence detections of nitroaromatic compounds and metal ions were performed with 1. 1 could detect the nitrophenol compounds and metal ions in water via luminescence quenching. The detection limits were 6.84 µM for 4-nitrophenol (NP), 1.85 µM for 2,4-dinitrophenol (DNP) and 2.76 µM for 2,4,6-trinitrophenol (TNP) and 94.4 µM for Al3+, 66 µM for Cr3+, 18.3 µM for Fe3+ and 27.6 µM for Cu2+. The detections of the nitrophenol compounds by 1 were due to hydrogen bonding interaction and resonance energy transfer. Moreover, the detections of metal ions by 1 were assigned to competitive absorption and electrostatic interactions with the anionic framework.