Dual-emitting metal–organic frameworks for ratiometric fluorescence detection of fluoride and Al3+ in sequence

Fluoride (F-) and Al3+ are two common ions existing in drinking water and natural water bodies. Excessive intake of F- can lead to serious health issues such as fluorosis and bone diseases while accumulated consumption of Al3+ may cause neurotoxicity-based diseases. Developing a fast, reliable, and sensitive sensor for visually detecting both F- and Al3+ is of great significance. In the present work, a ratiometric fluorescence sensor was constructed by incorporating rhodamine B (RhB) in situ into a zirconium-based metal-organic framework, UiO-66-NH2. The obtained nanocomposite UiO-66-NH2@RhB exhibited similar octahedral structure to UiO-66-NH2 with high BET surface area, and showed two emission peaks at 450 nm and 585 nm. The blue fluorescence from UiO-66-NH2 was enhanced by the addition of F- while subsequent Al3+ addition diminished the increased fluorescence intensity, and the red emission from RhB as the reference remained unchangeable to improve the detection precision. Under optimal conditions, detection of limits as low as 1.55 μM for F- and 0.54 μM for Al3+ in aqueous solution were achieved with good selectivity. High recoveries in drinking water samples were also acquired, showing potential applications of this ratiometric fluorescence sensor for practical evaluation of F- and Al3+.