Amino-Functionalized Single-Lanthanide Metal–Organic Framework as a Ratiometric Fluorescent Sensor for Quantitative Visual Detection of Fluoride Ions

Excessive content of fluoride ions (F–) in water will lead to water pollution and endanger human health, so the research on the method of low-cost, rapid, and efficient detection of F– is of particular significance. In this work, an amino-functionalized ligand with an appropriate triplet energy excited state, 2′-amino-[1,1′:4′,1″-terphenyl]-3,3″,5,5″-tetracarboxylic acid (H4TPTC-NH2), was selected to construct a luminescent single-lanthanide metal–organic framework, EuTPTC-NH2, with uncoordinated amino groups for the detection of F–. Based on host–guest interactions, that is, hydrogen bonds formed between the free amino groups and F– ions, EuTPTC-NH2 was developed as a ratiometric fluorescence probe for F– detection with good anti-interference ability, low detection limit, high water stability, and selectivity. It was found that EuTPTC-NH2 has an excellent linear response to F– in the concentration range of 0–80 μM with high sensitivity and a low detection limit of 11.26 μM. A hydrogel membrane based on the combination of EuTPTC-NH2 and agarose was also prepared for the quantitative visual detection of F– in water.