Sm/Cd-CPs with Dual-Core Clusters as High-Performance Multifunctional Fluorescence Sensors for Real-Time Detection of Fe³⁺, Cr₂O₇^2–, Nitrobenzene in Water

In light of the escalating water pollution problem, there is an urgent need to construct novel sensing materials capable of swift and real-time detection of pollutants. Coordination polymers (CPs) are widely used in the field of fluorescence sensing due to their special and novel structural characteristics. Here, the ligands 5-[(4-pyridyl)methoxy]isophthalic acid (H₂PLIA) and 4,4-bis(imidazolyl)biphenyl (BIBP) with high symmetry are employed as precursors to synthesize luminescent CPs [Sm(PLIA)_1.5(H₂O)₂]_<i>n</i> (CP1) and [Cd₂(PLIA)₂(BIBP)(H₂O)₂]_<i>n</i> (CP2) under solvothermal conditions. CP1 and CP2 are characterized by single-crystal X-ray diffraction, powder X-ray diffraction (PXRD), infrared spectroscopy (FT-IR), thermogravimetric (TG) analysis, and fluorescence spectrophotometry. Notably, the two CPs have different structural characteristics. CP1 presents a three-dimensional network structure, while CP2 presents a two-dimensional structure. And they have ideal thermodynamic and chemical stability as well as strong fluorescence performance. Fluorescence sensing tests showed that CP1 and CP2 have superior fluorescence recognition ability for Fe³⁺, Cr₂O₇^2-, and NB (nitrobenzene) in aqueous solution, with fast response time, strong selectivity, and high sensitivity. The possible mechanism of fluorescence recognition is due to the competitive absorption between CP1 and CP2 sensors and Fe³⁺, Cr₂O₇^2-, and NB in a water environment. These results provide valuable information for the multifunctional real-time fluorescence sensing platform for the detection of environmental pollutants in water bodies.