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

Abstract

High-performance fluorescence sensors combining convenience, low cost and high sensitivity are prospective 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 by polycarboxylic O-donor ligand. It showed 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 be highly sensitive and selectively detect trace amounts of Fe³⁺ and Cu²⁺ ions in an 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 stipulated for drinking water by the World Health Organization (WHO) (0.3/2.0 ppm) and U.S. Environmental Protection Agency (USEPA) (0.3/1.2 ppm). Moreover, LCU-109 also shows 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 is 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 for energy competitive absorption and weak interaction is further revealed.