A Cd-MOF fluorescence sensor with dual functional sites for efficient detection of metal ions in multifarious water environments

High performance fluorescence sensors combining convenience, cheapness and high sensitivity are crying out for water pollution and human health. Luminescent metal–organic frameworks (LMOFs) as sensors can meet these criteria for high efficient detection of toxic metal ions. Herein, a new LMOF LCU-109 has been fabricated by Sharpless in situ tetrazole synthesis system assisted with polycarboxylic O-donor ligand. It shows a 2D binodal (3,6)-connected kgd structure with multiple N and O dual functional sites for detecting guest metal ions. As expected, LCU-109 can highly sensitive and selective detect trace amounts of Fe3+ and Cu2+ ions in aqueous solution by the luminescence quenching mechanism. Notably, the detection limits (LODs) of Fe3+ and Cu2+ ions are 0.0043 and 0.0028 ppm respectively in water, which are significantly lower than the minimum standards of drinking water stipulated by the World Health Organization (WHO) (0.3/2.0 ppm) and U.S. Environmental Protection Agency (USEPA) (0.3/1.2 ppm). Meanwhile, LCU-109 also executes excellent luminescent sensing activities for Fe3+ and Cu2+ ions in simulated HEPES biological system and actual river water with low LODs of 0.034/0.019 ppm and 0.0756/0.107 ppm, respectively, which also lower than the standard of WHO and USEPA. Moreover, convenient and real-time naked eye detection effects are provided by the exquisitely made LCU-109 fluorescent test papers. Importantly, combining density functional theory (DFT) calculations with a variety of experiments, the fluorescence quenching mechanism of energy competitive absorption and weak interaction is further revealed.