PO₄^3– Ions Detection Based on UiO–66–NH₂@Eu–MOFs Ratio Fluorescent Probes

Using blue-emitting UiO–66–NH₂ with red-emitting Eu–MOF as fluorescence groups, a ratio fluorescence probe (UiO–66–NH₂@Eu–MOF) was constructed and successfully applied to the determination of trace PO₄^3– ions in environmental water samples. A ratiometric fluorescent probe for the determination of trace PO₄^3– ions in environmental water samples was constructed via combining blue-emitting UiO–66–NH₂ with red-emitting Eu–MOF. As PO₄^3– ions concentration increases, the coupling of PO₄^3– ions with Zr⁴⁺ ions in UiO–66–NH₂ leads to a weakened ligand–metal charge transfer effect, effectively restoring the luminescence of UiO–66–NH₂. Also, an intense coordination of Eu³⁺ ions with PO₄^3– ions can hinder the ligand–metal energy transfer, destroy the "antenna" effect, and lead to the quenching of Eu–MOF fluorescence. Under optimal conditions, a ratio of the fluorescence intensity at 445 nm to the fluorescence intensity at 633 nm is linearly related to PO₄^3– ions concentration in the range of 1–12 μmol/L. The sensor constructed has a good selectivity and accuracy, thus providing an effective way for the rapid detection of PO₄^3– ions.