Visual Detection of Fluoride Anions Using Mixed Lanthanide Metal–Organic Frameworks with a Smartphone

Abstract

Fluoride ion (F–) is one of the most harmful elements in drinking water. Over-intake of F– can result in dental fluorosis, kidney failure, or DNA damage. Therefore, developing affordable, equipment-free, and reliable methods for F– detection is an important goal. In this work, a series of mixed lanthanide metal–organic frameworks were synthesized using a triazine-based planar ligand, 4,4′,4″-s-triazine-2,4,6-triyltribenzoate (TATB) and mixed lanthanide ions (Tb3+ and Eu3+). The luminescent color of the Tb/Eu(TATB) can be finely modulated by changing the Tb3+/Eu3+ ratio in the synthesis procedure. Benefiting from the unique host–guest interaction (e.g., Lewis acid–base interaction), between F– and MOF host, a highly selective, sensitive, and reliable fluoride sensor was then developed. Moreover, visual detection of F– was achieved with a smartphone by identifying the RGB value. Drinking water samples were analyzed for F–, and the results obtained by our ratiometric luminescent method were consistent with those by ion chromatographic strategy. This easy-to-use sensor provides reliable detection of F– in everyday applications for nonexpert users, especially in remote rural areas.